Leary was born in Springfield, Massachusetts, the only child of an Irish American dentist who abandoned his wife Abigail Ferris and the rest of the family when Leary was thirteen. Leary graduated from Springfield's Classical High School.

In 1940, Leary enrolled as a cadet in the United States Military Academy at West Point. After violating the Academy’s honor code for allegedly drinking whiskey and lying about it , Leary was informally punished by being ‘silenced’, whereby he was shunned and ignored by his co-cadets as a tactic to pressure him to resign. The alleged incident was dismissed by the official court-martial, however the 'silencing' continued. After nine months, Leary was asked to resign by the honor committee, which he accepted. Almost fifty years later, Leary would remark that it was “the only fair trial I’ve had in a court of law”.

Leary spent two years at the College of the Holy Cross in Worcester, Massachusetts, transferred to University of Alabama where he received a bachelor's degree in psychology in 1943. His obituary in the New York Times said he "finally earned his bachelor's degree in the U. S. Army during World War II," when he was a sergeant in the Medical Corps. He received his master's degree at Washington State University in 1946, and his Ph.D. in psychology at the University of California, Berkeley in 1950. The title of Leary's Ph.D. dissertation was "The Social Dimensions of Personality: Group Structure and Process." He became an assistant professor at Berkeley (1950—1955), director of psychiatric research at the Kaiser Family Foundation (1955—1958), and a lecturer in psychology at Harvard University (1959—1963). He was fired from Harvard for failing to conduct his scheduled class lectures, though he claimed that he had fulfilled all of his teaching obligations. The decision to dismiss him was allegedly influenced by his role in the popularity of then-legal psychedelic substances among Harvard students and faculty members.

Leary's early work in psychology expanded on the research of Harry Stack Sullivan and Karen Horney regarding the importance of interpersonal forces in mental health. Leary focused on how the interpersonal process might be used to diagnose disorders and patterns found in human personalities. He developed a complex and respected interpersonal circumplex model, published in The Interpersonal Diagnosis of Personality,which offered a means by which psychologists could use MMPI scores to determine a respondent's characteristic interpersonal modes of reaction.

Leary married Marianne Busch in 1945. In 1947 while working on his PhD at the University of California at Berkeley, his wife gave birth to their first child, Susan, followed two years later by a son, Jack. In 1952 the Leary family spent a year in Spain, subsisting on a research grant awarded to Leary. A Berkeley colleague of Leary’s, Marv Freedman later recounted that “Something had been stirred in him in terms of breaking out of being another cog in society”.

In 1955, Leary's wife committed suicide, leaving him to raise their son and daughter alone. When Leary was 35 years old he described himself as "an anonymous institutional employee who drove to work each morning in a long line of commuter cars and drove home each night and drank martini ... like several million middle-class, liberal, intellectual robots."

On May 13, 1957, Life magazine published an article by R. Gordon Wasson that documented the use of psilocybin mushrooms in the religious ceremony of the indigenous Mazatec people of Mexico. Anthony Russo, a colleague of Leary's, experienced psychedelic (or entheogenic) Psilocybe mexicana mushrooms during a trip to Mexico, and related the experience to Leary. In August 1960, Leary traveled to Cuernavaca, Mexico with Russo and ate psilocybin mushrooms for the first time, an experience that drastically altered the course of his life. In 1965, Leary commented that he "learned more about... (his) brain and its possibilities... (and) more about psychology in the five hours after taking these mushrooms than... (he) had in the preceding fifteen years of studying and doing research in psychology."

Upon his return from Mexico to Harvard in 1960, Leary and his associates, notably Richard Alpert (later known as Ram Dass), began a research program known as the Harvard Psilocybin Project. The goal was to analyze the effects of psilocybin on human subjects (in this case, prisoners, and later, students of the Andover Newton Theological Seminary) using a synthesized version of the then-legal drug...one of two active compounds found in a wide variety of hallucinogenic mushrooms including Psilocybe mexicana. The compound was produced according to a process developed by Albert Hofmann of Sandoz Pharmaceuticals, famous for synthesizing LSD.

Beat poet Allen Ginsberg asked Leary to participate in the experiments after hearing about the Harvard research project. Leary was inspired by Ginsberg's enthusiasm and the two shared an optimism in the benefit of psychedelic substances to help people ‘turn on’ (discover a higher level of consciousness). Together they began a campaign of introducing other intellectuals and artists to psychedelics.

Leary argued that psychedelic substances, used at proper dosages, in a stable set and setting could, under the guidance of psychologists, alter behavior in beneficial ways not easily attainable through regular therapy. Leary's research focused on treating alcoholism and reforming criminals. Many of Leary's research participants reported profound mystic and spiritual experiences, which they claim permanently altered their lives in a very positive manner. According to Leary's autobiography, Flashbacks, LSD was given to 300 professors, graduate students, writers and philosophers and 75 percent of the test subjects reported the experience as one of the most educational and revealing experiences of their lives.

The Concord Prison Experiment was designed to evaluate how the effects of psilocybin combined with psychotherapy would rehabilitate prisoners upon being released. After being guided through the psychedelic experience ('trips') by Leary and his associates, 36 prisoners allegedly repented and swore to give up future criminal activity. For prisoners in USA, the average recidivism rate is 60 percent; the recidivism rate of the subjects involved in Leary's project dropped to 20 percent. The Concord Prison experiment demonstrated that long-term reduction in overall criminal recidivism rates could be achieved with a combination of psilocybin-assisted group psychotherapy (inside the prison) along with a comprehensive post-release follow-up support program modeled on Alcoholics Anonymous. The study concluded that psilocybin-assisted group psychotherapy and a post-release program would significantly reduce recidivism rates. No further study or experiment took place as psilocybin was declared to be a dangerous substance with no medical benefits by the Drug Enforcement Agency of USA.

Leary and Alpert founded the International Foundation for Internal Freedom in 1962 in Cambridge, Massachusetts. This was run by Lisa Bieberman (now known as Licia Kuenning), a disciple of Leary and one of his many lovers. Their research attracted a great deal of public attention and, as a result, many people wanted to participate in the experiments, but were unable to do so because of the high demand. In order to satisfy the curiosity of those who were turned away, a black market for psychedelics developed near the Harvard University Campus.

According to Andrew Weil, Leary was fired for not showing up to his lecture classes, while Alpert was fired for allegedly giving psilocybin to an undergraduate in an off-campus apartment. This version is supported by the words of Harvard President Nathan M. Pusey, who, regarding Leary's termination, released the following statement on May 27, 1963:

"On May 6, 1963, the Harvard Corporation voted, because Timothy F. Leary, lecturer on clinical psychology, has failed to keep his classroom appointments and has absented himself from Cambridge without permission, to relieve him from further teaching duty and to terminate his salary as of April 30, 1963."

Leary's activities interested siblings Peggy, Billy and Tommy Hitchcock, heirs to the Mellon fortune, who in 1963 helped Leary and his associates acquire the use of a rambling mansion on an estate in the town of Millbrook (near Poughkeepsie, New York), where they continued their experiments. Leary later wrote:

"We saw ourselves as anthropologists from the twenty-first century inhabiting a time module set somewhere in the dark ages of the 1960s. On this space colony we were attempting to create a new paganism and a new dedication to life as art."

Later, the Millbrook estate was described by Luc Sante of The New York Times as:

"the headquarters of Leary and gang for the better part of five years, a period filled with endless parties, epiphanies and breakdowns, emotional dramas of all sizes, and numerous raids and arrests, many of them on flimsy charges concocted by the local assistant district attorney, G. Gordon Liddy."

Others contest this characterization of the Millbrook estate; for instance, in The Electric Kool-Aid Acid Test, Tom Wolfe portrays Leary as only interested in research, and not using psychedelics merely for recreational purposes. According to "The Crypt Trip" chapter of Wolfe's book, when Ken Kesey's Merry Pranksters visited the residence, the Pranksters did not even see Leary, who was engaged in a three-day trip. According to Wolfe, Leary's group even refused to give the Pranksters acid.

In 1964, Leary co-authored a book with Alpert and Ralph Metzner called The Psychedelic Experience, based upon the Tibetan Book of the Dead. In it, they wrote:

"A psychedelic experience is a journey to new realms of consciousness. The scope and content of the experience is limitless, but its characteristic features are the transcendence of verbal concepts, of spacetime dimensions, and of the ego or identity. Such experiences of enlarged consciousness can occur in a variety of ways: sensory deprivation, yoga exercises, disciplined meditation, religious or aesthetic ecstasies, or spontaneously. Most recently they have become available to anyone through the ingestion of psychedelic drugs such as LSD, psilocybin, mescaline, DMT, etc. Of course, the drug does not produce the transcendent experience. It merely acts as a chemical key...it opens the mind, frees the nervous system of its ordinary patterns and structures."

Repeated FBI raids ended the Millbrook era. Regarding a 1966 raid by G. Gordon Liddy, Leary told author and Prankster Paul Krassner: "He was a government agent entering our bedroom at midnight. We had every right to shoot him. But I've never owned a weapon in my life. I have never had and never will have a gun around."

On September 19, 1966, Leary founded the League for Spiritual Discovery, a religion declaring LSD as its holy sacrament, in part as an unsuccessful attempt to maintain legal status for the use of LSD and other psychedelics for the religion's adherents, based on a "freedom of religion" argument. (Although The Brotherhood of Eternal Love would subsequently consider Leary their spiritual leader, The Brotherhood did not evolve out of IFIF International Foundation for Internal Freedom.) On October 6, 1966, LSD was made illegal in the United States and controlled so strictly that not only were possession and recreational use criminalized, but all legal scientific research programs on the drug in the US were shut down as well.

In 1966, Folkways Records recorded Leary reading from his book The Psychedelic Experience, and released the album, The Psychedelic Experience: Readings from the Book "The Psychedelic Experience. A Manual Based on the Tibetan...".

During late 1966 and early 1967, Leary toured college campuses presenting a multi-media performance "The Death of the Mind", which attempted to artistically replicate the LSD experience. Leary said the League for Spiritual Discovery was limited to 360 members and was already at its membership limit, but he encouraged others to form their own psychedelic religions. He published a pamphlet in 1967 called Start Your Own Religion, to encourage people to do so (see below under "writings").

Leary was invited to attend the January 14, 1967 Human Be-In by Michael Bowen the primary organizer of the event. Leary spoke at the Human Be-In, a gathering of 30,000 hippies in Golden Gate Park in San Francisco and uttered his famous phrase, "Turn on, tune in, drop out". The phrase came to him in the shower one day after Marshall McLuhan suggested to Leary that he should come up with "something snappy" to promote the benefits of LSD.

At some point in the late 1960s, Leary moved to California. He made a number of friends in Hollywood. "When he married his third wife, Rosemary Woodruff in 1967, the event was directed by Ted Markland of Bonanza. All the guests were on acid."

In the late 1960s and early 1970s, Leary (in collaboration with the writer Brian Barritt) formulated his circuit model of consciousness, in which he claimed that the human mind/nervous system consisted of seven circuits which, when activated, produce seven levels of consciousness (this model was first published as the short essay, "The Seven Tongues of God"). The system soon expanded to include an eighth circuit; this version was first unveiled to the world in the rare 1973 pamphlet "Neurologic" (written with Joanna Leary while he was in prison), but was not exhaustively formulated until the publication of Exo-Psychology (by Leary) and in Robert Anton Wilson's Cosmic Trigger in 1977. Wilson contributed significantly to the model after befriending Leary in the early 1970s, and has used it as a framework for further exposition in his book Prometheus Rising, among other works.

Leary believed that the first four of these circuits ("the Larval Circuits" or "Terrestrial Circuits") are naturally accessed by most people in their lifetimes, triggered at natural transition points in life, such as puberty. The second four circuits ("the Stellar Circuits" or "Extra-Terrestrial Circuits"), Leary claimed, were evolutionary off-shoots of the first four that would be triggered at transition points that we will have when we evolve further, and would equip us to encompass life in space, as well as the expansion of consciousness that would be necessary to make further scientific and social progress. Leary suggested that some people may "shift to the latter four gears" (i.e. trigger these circuits artificially) by utilizing consciousness-altering techniques such as meditation and spiritual endeavors such as yoga, or by taking psychedelic drugs specific to each circuit. An example of the information Leary cited as evidence for the purpose of the "higher" four circuits was the feeling of floating and uninhibited motion experienced by users of marijuana. In the eight circuit model of consciousness, a primary theoretical function of the fifth circuit (the first of the four developed for life in outer space) is to allow humans to become accustomed to life in a zero or low gravity environment.

Leary's first run-in with the law came on December 20, 1965. Leary decided to take his children and Rosemary to Mexico for an extended stay to write a book. During a border crossing with his girlfriend Rosemary Woodruff and two children Jack and Susan from Mexico into the United States, marijuana was found in his daughter Susan's underwear. They had crossed into Laredo, Mexico in the late afternoon and discovered they would have to wait until morning for the appropriate visa for an extended stay. They decided to cross back into Texas to spend the night and were on the bridge when Rosemary remembered she had a very small amount of marijuana in her possession. It was impossible to throw it out on the bridge so Susan put it in her underwear. After taking responsibility for the controlled substance, Leary was convicted of possession under the Marihuana Tax Act on March 11, 1966, and sentenced to 30 years in jail, given a $30,000 fine and ordered to undergo psychiatric treatment. Soon after, however, he appealed the case, claiming the Marihuana Tax Act was, in fact, unconstitutional, as it required a degree of self-incrimination. Leary claimed this was in stark violation of the Fifth Amendment. On December 26, 1968, Leary was arrested again, in Laguna Beach, California, this time for the possession of two roaches of marijuana, which Leary claimed were planted by the arresting officer. He was later convicted of this offense. On May 19, 1969, The Supreme Court concurred with Leary in Leary v. United States. The Marihuana Tax Act was declared unconstitutional, and his 1965 conviction was quashed. On the day his conviction was overturned, Leary announced his candidacy for Governor of California, running against Ronald Reagan. His campaign slogan was "Come together, join the party." On June 1, 1969, Leary joined John Lennon and Yoko Ono at their Montreal Bed-In and Lennon subsequently wrote Leary a campaign song called "Come Together".

On January 21, 1970, Leary received a ten-year sentence for his 1968 offense, with a further ten added later while in custody, for a previous arrest in 1965, twenty years in total to be served consecutively for less than a half ounce of marijuana. When Leary arrived in prison, he was given psychological tests that were used to assign inmates to appropriate work details. Having designed some of the tests himself (including the "Leary Interpersonal Behavior Test"), Leary answered them in such a way that he seemed to be a very conforming, conventional person with a great interest in forestry and gardening. As a result, Leary was assigned to work as a gardener in a lower security prison, and in September 1970 he escaped. Leary claimed his non-violent escape was a humorous prank, and left a challenging note for the authorities to find after he was gone. For a fee, paid by The Brotherhood of Eternal Love, the Weathermen smuggled Leary and his wife, Rosemary Woodruff Leary, out of the United States and into Algeria. He sought the patronage of Eldridge Cleaver and the remnants of the separatist USA Black Panther party’s "government in exile." After staying with them for a short time, Leary claimed that Cleaver attempted to hold him and his wife hostage.

In 1971, the couple fled to Switzerland, "where they were sheltered and effectively imprisoned by a large-living arms dealer, Michel Hauchard, who claimed he had an 'obligation as a gentleman to protect philosophers,' but mostly had a film deal in mind." In 1972, President Richard Nixon's attorney general, John Mitchell, persuaded the Swiss government to imprison Leary, which it did for a month, but the Swiss refused to extradite him back to the U.S. In that same year, Leary and Rosemary separated. Leary became involved with Swiss-born British socialite Joanna Harcourt-Smith, a stepdaughter of financier Árpád Plesch. Leary "married" Harcourt-Smith at a hotel two weeks after they were first introduced; she used his surname until their breakup in early 1977. They traveled to Vienna, then Beirut and finally went to Kabul, Afghanistan, in 1973. "Afghanistan had no extradition treaty with the United States, but this stricture did not apply to American airliners," Luc Sante wrote in a review of a biography of Leary. That interpretation of the law was used by U.S. authorities to capture the fugitive. "Before Leary could deplane, he was arrested by an agent of the federal Bureau of Narcotics and Dangerous Drugs."

At a layover in the United Kingdom, as Leary was being flown back to the United States, he requested political asylum from Her Majesty's Government, but to no avail. He was then held on five million dollars bail ($21.5 mil. in 2006). President Richard Nixon had earlier labeled him "the most dangerous man in America." The judge at his remand hearing remarked, "If he is allowed to travel freely, he will speak publicly and spread his ideas." Facing a total of 95 years in prison, Leary hired criminal defense attorney Bruce Margolin and was put into solitary confinement in Folsom Prison, California, where at one point he was in a cell immediately adjacent to Charles Manson.

Leary made somewhat of a pretense of cooperating with the FBI's investigation of the Weathermen and radical attorneys, by giving them information that they already had or that was of little consequence; in response, the FBI gave him the code name "Charlie Thrush".

Leary would later claim, and members of the Weathermen would later support, that no one was ever prosecuted based on any information he gave to the FBI.

"The Weather Underground, the radical left organization responsible for his escape, was not impacted by his testimony. Histories written about the Weather Underground usually mention the Leary chapter in terms of the escape for which they proudly took credit. Leary sent information to the Weather Underground through a sympathetic prisoner that he was considering making a deal with the FBI and waited for their approval. The return message was 'we understand.'"

While imprisoned Leary remained a productive writer, sowing the seeds for his incarnation as a futurist lecturer with the StarSeed Series. In Starseed (1973), neurologic (1973), & Terra II: A Way Out (1974), Leary transitioned from Eastern philosophy and Aleister Crowley to a belief that outer space was a medium for spiritual transcendence as his principal frame of reference. Neurologic also added the idea of "time dilation/contraction" available to the activated brain through the cellular, DNA, or atomic level of reality. Terra II is his first detailed proposal for space colonization. Leary’s muse peaked with Exo...Psychology, Neuropolitics, and Intelligence Agents.

Leary was released from prison on April 21, 1976, by Governor Jerry Brown. After briefly relocating to San Diego, Leary established residence in Laurel Canyon and continued to write books and appear as a lecturer and (by his own terminology) "stand-up philosopher." In 1978, Leary married filmmaker Barbara Blum, also known as Barbara Chase, sister of actress Tanya Roberts. Leary adopted Blum's son and raised him as his own. Leary and Blum divorced in 1992.

Leary cultivated a friendship with former foe G. Gordon Liddy, the notorious Watergate burglar and conservative radio talk-show host. They toured the lecture circuit in 1982 as ex-cons (Liddy having been imprisoned after high-level involvement in the Watergate scandal) debating about the soul of America. The tour generated massive publicity and considerable funds for both figures. Along with the personal appearances, a successful documentary called Return Engagement that chronicled the tour, and the concurrent release of the autobiography Flashbacks, helped to return Leary to the spotlight.

While his stated ambition was eventually to cross over as a mainstream Hollywood personality, reluctant studios and sponsors ensured that that never occurred. Nonetheless, constant touring ensured that he was able to maintain a very comfortable lifestyle by the mid-1980s, while his colorful past made him a desirable guest at A-list parties throughout the decade. He also attracted a more intellectual crowd, which included John Frusciante (Leary appeared in Johnny Depp's and Gibby Haynes' 1994 film Stuff which showed the squalid conditions that Frusciante was living in at the time), Robert Anton Wilson, David Byrne, science fiction wunderkind William Gibson, and Norman Spinrad amongst its ranks.

While he continued to use drugs frequently on a private basis, rather than evangelizing and proselytizing the use of psychedelics as he had in the 1960s, the latter day Leary emphasized the importance of space colonization and an ensuring extension of the human lifespan while also providing a detailed explanation of the eight-circuit model of consciousness in books such as Info-Psychology, among several others. He adopted the acronym "SMI²LE" as a succinct summary of his pre-transhumanist agenda: SM (Space Migration) + I² (intelligence increase) + LE (Life extension). Leary credited L5 co-founder Keith Henson with helping develop his interest in space migration.

Leary's colonization plan varied greatly throughout the years. Because he believed that he would soon migrate into space, Leary was opposed to the ecology movement. He dismissed many of Earth’s problems and labeled the entire field of ecology “a seductive dinosaur science.” Leary stated that only the “larval,” intellectually and philosophically backward humans, would choose to remain in “the fouled nest.” According to his initial plan to leave the planet, 5,000 of Earth's most virile and intelligent individuals would be launched on a vessel (Starseed 1) equipped with luxurious amenities. This idea was inspired by the plotline of Paul Kantner's concept album Blows Against The Empire, which in turn was derived from Robert A. Heinlein's Lazarus Long series. In the 1980s, he came to embrace NASA scientist Gerard O'Neill's more realistic and egalitarian plans to construct giant Eden-like High Orbital Mini-Earths (documented in the Robert Anton Wilson lecture H.O.M.E.s on LaGrange) using existing technology and raw materials from the Moon, orbital rock and obsolete satellites.

By the mid 1980s, Leary had begun to incorporate computers, the Internet, and virtual reality into his aegis of thought. Leary established one of the earliest sites on the World Wide Web, and was often quoted describing the Internet as "the LSD of the 1990s." He became a promoter of virtual reality systems, and sometimes demonstrated a prototype of the Mattel Power Glove as part of his lectures (as in From Psychedelics to Cybernetics). Around this time he cultivated friendships with a number of notable people in the field, including Brenda Laurel, a pioneering researcher in virtual environments and human—computer interaction. With the rise of cyberdelic counter-culture, Leary became a consultant to Billy Idol in the production of the latter's 1993 album, Cyberpunk.

In 1990, Leary's daughter, Susan, committed suicide after years of mental instability. After separating from Barbara Leary in 1992, Leary began to associate with a much younger, artistic and tech-savvy crowd that included people as diverse as actors Johnny Depp, Susan Sarandon and Dan Aykroyd, and his granddaughters, Dieadra Martino and Sara Brown; grandson, Ashley Martino; son, Zach Leary; author Douglas Rushkoff, publisher Bob Guccione, Jr., and goddaughters: actress Winona Ryder and artist/music-photographer Hilary Hulteen. In spite of his declining health, Leary maintained a regular schedule of public appearances through 1994.

From 1989 on, Leary had begun to reestablish his connection to non-mainstream religious movements with an interest in altered states of consciousness. In 1989 he appeared with friend and book collaborator Robert Anton Wilson in a dialog entitled The Inner Frontier for the Association for Consciousness Exploration, a Cleveland-based group that had been responsible for his first Cleveland, Ohio appearance in 1979. After that, he appeared at the Starwood Festival, a major Neo-Pagan event run by ACE, in 1992 and 1993 The Cleveland Free Times :: Archives :: Circle Of Ash (though his planned 1994 WinterStar Symposium appearance was cancelled due to his declining health). In front of hundreds of neo-pagans in 1992, he declared, "I have always considered myself, when I learned what the word meant, I've always considered myself a Pagan." He also collaborated with Eric Gullichsen on Load and Run High-tech Paganism: Digital Polytheism.

In early 1995, Leary discovered he was terminally ill with inoperable prostate cancer. He did not reveal the condition to the press upon diagnosis, but did so after the death of Jerry Garcia in August.

Leary authored an outline for a book called Design for Dying, which attempted to show people a new perspective of death and dying. Leary's de facto "family"...his staff of technophilic Gen X...updated his website on a daily basis as a sort of proto-blog, noting his daily intake of various illicit and legal chemical substances, with a predilection for nitrous oxide, cigarettes, his trademark "Leary Biscuits" (a snack cracker with cheese and a small marijuana bud, briefly microwaved), and eventually heroin and morphine. His sterile house was completely redecorated by the staff, who had more or less moved in, with an array of surreal ornamentation. In his final months, thousands of visitors, well wishers and old friends visited him in his California home. Until the final weeks of his illness, Leary gave many interviews discussing his new philosophy of embracing death.

For a number of years, Leary was reported to have been excited by the possibility of freezing his body in cryonic suspension, and Leary publicly announced in September 1988 that he had signed up with Alcor. Leary had appeared at Alcor's grand opening a year previously. He did not believe that he would be resurrected in the future, but he believed that cryonics had important possibilities and stated the chance was "one chance in 1,000". He called it his "duty as a futurist," and helped publicize the process and hoped it would work for his children and grandchildren if not for him, although he said he was "light-hearted" about it. Leary had relationships with two cryonic organizations, originally Alcor and then CryoCare, which delivered a cryonic tank to Leary's house in the months before his death. However, Leary subsequently requested that his body be cremated, which it was, and distributed among his friends and family.

Leary's death was videotaped for posterity at his request, capturing his final words. During his final moments, he said, "Why not?" to his son Zachary. He uttered the phrase repeatedly, in different intonations, and died soon after. His last word, according to Zachary Leary, was "beautiful."

The film Timothy Leary's Dead (1996) contains a simulated sequence in which Leary allows his bodily functions to be suspended for the purposes of cryonic preservation, and his head is removed and placed on ice. At the end of the film is a sequence showing the creation of the artificial head used in the film.

Seven grams of Leary's ashes were arranged by his friend at Celestis to be buried in space aboard a rocket carrying the remains of 24 other people including Gene Roddenberry (creator of Star Trek), Gerard O'Neill (space physicist), Krafft Ehricke (rocket scientist), and others. A Pegasus rocket containing their remains was launched on April 21, 1997, and remained in orbit for six years until it burnt up in the atmosphere.

Leary is often considered one of the most prominent figures during the counterculture of the 1960s, and since those times has remained incredibly influential on pop culture, literature, television, film; and especially music.

Timothy Leary's ideas heavily influenced the work of Robert Anton Wilson. This influence went both ways and Leary admittedly took just as much from Wilson. Wilson's book Prometheus Rising was an in depth, highly detailed and inclusive work documenting Leary’s eight circuit model of consciousness. Although the theory originated in discussions between Leary and a Hindu holy man at Millbrook, Wilson was one of the most ardent proponents of it and introduced the theory to a mainstream audience in 1977's bestselling Cosmic Trigger. In 1989, they appeared together on stage in a dialog entitled The Inner Frontier in Cleveland, Ohio hosted by the Association for Consciousness Exploration, (the same group that had hosted Leary's first Cleveland appearance in 1979). Wilson and Leary conversed a great deal on philosophical, political and futurist matters and became close friends who remained in contact through Leary's time in prison and up until his death. Wilson regarded Leary as a brilliant man and often is quoted as saying (paraphrase) "Leary had a great deal of 'hilaritas', the type of cheer and good humour by which it was said you could recognise a deity".

Leary's apparent endorsement of care-free LSD usage is also reflected upon in a more negative light in Hunter S. Thompson's Fear and Loathing in Las Vegas. In addition, Owsley Stanley, one of the pioneers of the era, would later write of him:

"Leary was a fool. Drunk with 'celebrity-hood' and his own ego, he became a media clown...and was arguably the single most damaging actor involved in the destruction of the evanescent social movement of the '60s. Tim, with his very public exhortations to the kids to 'tune in, turn on and drop out,' is the inspiration for all the current draconian US drug laws against psychedelics. He would not listen to any of us when we asked him to please cool it, he loved the limelight and relished his notoriety... I was not a fan of his."

Author and Merry Prankster Ken Kesey remained a supporter and admirer of Leary throughout his career,

"Leary can get a part of my mind that's kind of rusted shut grinding again, just by being around him and talking."

World religion scholar Huston Smith was turned on by Leary after the two were introduced to one another by Aldous Huxley in the early 1960s. The experience was interpreted as deeply religious by Smith, and is captured in detailed religious terms in Smith's later work Cleansing of the Doors of Perception. This was Smith's one and only entheogenic experience, at the end of which he asked Leary, to paraphrase, if Leary knew the power and danger of that with which he was conducting research. In Mother Jones Magazine, 1997, Smith commented:

"First, I have to say that during the three years I was involved with that Harvard study, LSD was not only legal but respectable. Before Tim went on his unfortunate careening course, it was a legitimate research project. Though I did find evidence that, when recounted, the experiences of the Harvard group and those of mystics were impossible to tell apart...descriptively indistinguishable...that's not the last word. There is still a question about the truth of the disclosure."

His popular slogan, "Turn on, tune in, drop out", signified a conceptual way of thinking wherein a person would turn on to their own way of thinking, tune in to themselves, and drop out of society. This constituted a concept of inward self reliance.

In popular culture

Music

The Psychedelic Experience was the inspiration for John Lennon's song "Tomorrow Never Knows" on The Beatles' album Revolver. Leary once recruited John Lennon to write a theme song for his California gubernatorial campaign (which was interrupted by his prison sentence), inspiring Lennon to come up with "Come Together", based on Leary's theme and catchphrase for the campaign. Leary was also present when Lennon and his wife Yoko Ono recorded Give Peace a Chance during one of their bed-ins in Montreal and is mentioned in the lyrics of the song. He appears in the world television broadcast of "All You Need is Love" as well.

While in exile in Switzerland, Leary and British writer Brian Barrett collaborated with the German band Ash Ra Tempel, and recorded the album Seven Up. He is credited as a songwriter, and his lyrics and vocals can be heard throughout the album. For some reason he left this experience out of his autobiography.

Leary was the explicit subject of the Ray Thomas-written The Moody Blues song "Legend of a Mind", which memorialized him with the words, "Timothy Leary's dead. No, no, no, no he's outside looking in" (a lyric later incorporated into the Bongwater's cover version of the Moody Blues song "Ride My See-Saw"). At first, Leary detested the line, but later found the sense of humor to adopt "Legend of a Mind" as his theme song when he hit the lecture circuit. Another Moody Blues song "When You're a Free Man" was written by Mike Pinder, and it detailed Leary's imprisonment, while also showing concern for his family ("How are the children, and Rosemary?).

Timothy Leary also worked with new wave band Devo, appearing as Dr. Byrthfood in a segment of their 1985 home video We're All Devo!. This segment would appear on The Complete Truth About De-Evolution as "Kindred Spirit". Leary and Devo also worked together on a planned video game adaptation of Neuromancer, though plans fell through.

A number of other musical groups have admired and been influenced by Leary, including:

• The song "Voyage 34" by Porcupine Tree which periodically has a snippet of a monologue by Timothy Leary.
• The song "Turn On, Tune In, Drop Out With Me," by the alternative rock band Cracker, paraphrases one of Leary's catchphrases in a song about physically escaping mainstream culture (from the album "Sunrise in the Land of Milk and Honey" (2009)).
• The song "Timothy Leary" by the alternative rock band Guster was on their 2007 release of Satellite EP as well as on the "Rock the Net" multi-artist compilation (2008).
• The progressive rock band Tool sampled one of his monologues during the opening of their live performances of the track "Third Eye" from the album Ænima, as heard in the live album Salival, released in 2000. More recently, a sample of one of Leary's monologues has been used right before the band takes the stage on their 2010 summer tour.
• The metal band Nevermore mentions Leary in their lyrics, and titled one of their albums "The Politics of Ecstasy" (1996) (after Leary's book of the same name). Also, on Nevermore's self-titled album (1995), there is a song named "Timothy Leary".
• The song "Texan Book of the Dead" by Clutch, released in 1995 on their self-titled album, mentions Leary in a round-about way. "Be leery of Timothy, Clear light and all that. If you want light go stare at the sun. Hell, that boy don't know crap."
• The Psychedelic Trance band Infected Mushroom uses a sound clip of Leary saying "Turn on, tune in, and drop out" in the song "Drop Out".
• Leary made a cameo appearance in "Stuff" (1993), a short film directed by Johnny Depp and Gibby Haynes about the Red Hot Chili Peppers' guitar player John Frusciante.
• Leary is also mentioned in the song "The Seeker" by The Who (1970): "I asked Bobby Dylan/ I asked the Beatles/ I asked Timothy Leary/ But he couldn't help me either", placing him among several other leading figures of '60s pop culture.
• References to Leary appear in the iconic counter-culture piece "Hair" in the lyrics to "Let the sunshine in" ("Singing our space songs on a spider web sitar / Life is around you and in you / Answer for Timothy Leary, dearie"), and in the song "Manchester England, England" [Now that I've dropped out/Why is life dreary, dreary?/Answer my weary query/Timothy Leary, dearie]. Also the song "Hare Krishna" has a small reference to Leary's catch phrase "Turn on, tune in, drop out": ("...Love / Love / Love / Love / Drop out / Drop out / Drop out / Drop out / Be in/ Be in/ Be in/ Be in").
• Leary waxed poetic about helicopters on "Gila Copter," the first track of the 1993 album "Linger Ficken' Good" by The Revolting Cocks, and also appeared in the music video for "Crackin' Up" from the same album.
• Tim played the father of Mike Muir in the music video "Possessed to Skate" from the album Join the Army by Suicidal Tendencies.
• UK electronic dance group, The Grid, sampled Leary in their 1990 track "Origins of Dance".
• Leary appeared in the 1995 video for the Blind Melon song "Galaxie".
• Leary is mentioned in the Dog Fashion Disco song "The Acid Memoirs"
• The song "Flash Delirium" by MGMT paraphrases Leary's catchphrase with the lyrics "So turn it on/ Tune it in/ and stay inert."
• Leary is mentioned in the Butthole Surfers song "Weird Revolution"

Television and film

Leary was the inspiration for the character "Brother William" in a 1968 episode of Dragnet. In the episode entitled "The Big Prophet," Jack Webb's character, Joe Friday, along with his partner Bill Gannon visit Brother William's home and spend the entire episode debating the consequences of using LSD and other drugs. Friday famously tells Brother William, "Marijuana is the flame, heroin is the fuse, LSD is the bomb." At the end of the episode Brother William is found guilty of selling narcotics to minors.

In the movie The Ruling Class, the character Jack Gurney (played by Peter O'Toole), who thinks he is Jesus, claims that the voice of "Timothy O'Leary" told him he was God. Leary also appeared in Cheech and Chong's Nice Dreams (1981) as a benevolent psychiatrist administering LSD to mental patients.

Leary had a brief voice-over appearance on the American sitcom Frasier in the episode "The Show where Lilith Comes Back" as Hank, a man with an overeating disorder who called into The Dr. Frasier Crane Show.

In Across the Universe , Bono (playing the character of "Dr. Robert") refers to Dr. Frank Geary, who is apparently an allusion to Dr. Timothy Leary.

In Warehouse 13 Timothy Leary's glasses are an artifact in the Warehouse which cause hallucinogenic visions when worn; the longer they are worn, the less the user wants to take them off. While wearing them, Agent Pete Lattimer sees his superior with a walrus head surrounded by bubbles. A knock-off pair were made by rogue agent James MacPherson to reveal the entrance to his underground hideout.

Had a cameo appearance in Abbe Wool's Roadside Prophets (1992), where he played the character "Salvadore," helping the two main characters fix a motorcycle and offering some insight into self-enlightenment.

Was interviewed on Cartoon Network's Space Ghost Coast to Coast in 1994 (episode 3, "Elevator").

Leary made a cameo in the 1989 film Rude Awakening.

In the 2009 film The Men Who Stare at Goats Bill (Jeff Bridges) awakes from a dream, or possible telepathic vision, and claims that he saw Timothy Leary, to which Bob Wilton (Ewan McGregor) replies "Timothy Leary's dead."

Leary authored and co-authored over twenty books and was featured on more than a dozen audio recordings. He had an acting career that included over a dozen appearances in movies and television shows, over thirty appearances as himself in the same, and produced and/or collaborated in both multi-media presentations and computer games.