Hartmann was born in Grand Rapids, Michigan, the son of an atheist father and a Christian mother, and grew up in nearby Lansing. Interested in politics from a young age, he reportedly campaigned for Barry Goldwater during the 1964 presidential election when he was 13. By 1968, Hartmann was studying at Michigan State University and working as a part-time news announcer at local country music station WITL while protesting the Vietnam War with Students for a Democratic Society (SDS).

While dropping out of Michigan State during the tumultuous late 1960s, Hartmann received his C.H. (Chartered Herbalist) degree from Dominion Herbal College, an M.H. (Master of Herbology) degree from Emerson College of Herbology, and a Ph.D. in Homeopathic Medicine from Brantridge in England. Brantridge, was considered by experts in the field to be a diploma mill. Hartmann says he never references these degrees on his radio or TV shows, and they do not appear on his official biography on his home page at thomhartmann.com. In a February 7 interview with Brian Lamb on C-SPAN, he mentioned that he did not place them in his Wikipedia entry, does not reference them in public, that Brantridge was a correspondence course, and he took them because he ran an herbal tea company at the time in the early 1970s and was interested in the topic of herbology and homeopathy. The reference appears only in the "About the author" section of his first book, ADD: A Different Perception. The section was commissioned by the publisher and written by Dave deBronkart.

Hartmann is considered to have progressive/liberal politics (although he describes himself as part of the radical middle). He is the author of numerous books including The Rise of Corporate Dominance and the Theft of Human Rights, in which he argues that the 1886 U.S. Supreme Court decision in Santa Clara County v. Southern Pacific Railroad Company (118 U.S. 394) did not actually grant corporate personhood, and that this doctrine derives from a mistaken interpretation of a Supreme Court clerk's notes. Hartmann considers this a clear contradiction of the intent of the Founding Fathers of the United States. He has also written on the separation of church and state, drawing upon the Federalist Papers to argue that the Founding Fathers warned against the notion of the United States being a Christian nation. He contends that the 2000 American election and 2004 American election were stolen through electronic tampering, denial of the voting franchise by rigged voting lists, and limiting availability of voting machines. He also accuses the Bush administration of eroding democracy and individual freedoms.

Hartmann is also a vocal critic of the effects of globalization on the U.S. economy, claiming that economic policies enacted during and since the presidency of Ronald Reagan have led, in large part, to many American industrial enterprises' being acquired by multinational firms based in overseas countries, leading in many cases to manufacturing jobs' — once considered a major foundation of the U.S. economy — being relocated to countries in Asia and other areas where the costs of labor are lower than in the U.S.; and the concurrent reversal of the United States' traditional role of a leading exporter of finished manufactured goods to that of a primary importer of finished manufactured goods (exemplified by massive trade deficits with countries such as China). Hartmann argues that this phenomenon is leading to the erosion of the American middle class, whose survival Hartmann deems critical to the survival of American democracy. This argument is expressed in Hartmann's 2006 book, Screwed: The Undeclared War Against The Middle Class and What We Can Do About It. One of the book's main arguments is that media deregulation leads to corporate media's shifting the American consensus towards the acceptance of privatization and massive corporate profits — which causes the shrinking of the middle class.

In his book Ultimate Sacrifice, he and the co-author argue that President John F. Kennedy's assassination resulted from a conspiracy among three mafia "godfathers" who took advantage of a proposed 1963 USA-sponsored coup (against Cuba's Fidel Castro) to kill the President and then hide their tracks in the resulting cover-up of the coup plans. Gore Vidal, in his recent autobiography "Point To Point Navigation" devotes much of the final two chapters of his book to praising Hartmann's and Lamar Waldron's scholarship in "solving" the JFK case (JFK was a friend of Vidal's).

Hartmann started in radio as a DJ (country, rock, progressive overnight) in 1968 in Lansing, Michigan, (on WITL, WVIC, WFMK) and program director (WNBY), and worked full or part-time in radio while also attending school and/or running businesses in Michigan for a decade. He returned to radio in February 2003 with a show on a local station in Vermont, then a month later picked up the noon-3 PM ET slot on the i.e. America Radio Network and Sirius Satellite Radio. In 2005, he moved from Vermont to Oregon and, in addition to continuing his national show, also hosted a local talk show in Portland, Oregon, from 2005 until early 2007 on KPOJ, an affiliate of Air America Radio owned by Clear Channel Communications. The KPOJ local morning 6 — 9 AM PT is now hosted by Carl Wolfson and Christine Alexander, with Hartmann as a daily participant in only the third (8 - 9 AM PT) hour before he begins his nationally syndicated program.

Hartmann's national program, on the air since 2003 in the noon — 3 PM ET daypart live against Rush Limbaugh, was chosen by Air America to replace Al Franken on most Air America affiliates in 2007. Air America sold; Al Franken quitting - Portland Business Journal: Some stations, such as The Quake in San Francisco, had already dropped or moved Franken for Hartmann, who now is, according to Talkers Magazine, America's most important liberal talker. As of October 2010, the show was carried on 72 terrestrial radio stations in 33 states, as well as on Sirius and XM satellite radio. A community radio station in Africa, Radio Builsa in Ghana, also broadcasts the show. Various local cable TV networks simulcast the program.

According to his syndicator Dial Global, more people listen to Hartmann's show on more stations than any other progressive talk show in America. The Thom Hartmann Show is estimated by industry magazine Talkers to have 2.75 million unique listers per week. In addition to Dial Global, a subsidiary of Triton Media Group, the show is now also offered via Pacifica Audioport to nonprofit stations in a nonprofit compliant format and is simulcast on Dish Network Channel 9415 via Free Speech TV Network.

He often debates members of the Ayn Rand Institute The Ayn Rand Institute: Thom Hartmann Interviews and conservatives. Several of his debates, including one involving Bill Bennett at The Heritage Foundation, were carried on C-Span, although most of them occur on his own radio program. The two regular guests on the program are sympathetic to Hartmann's political views. Sen. Bernie Sanders appears every Friday during the first hour of the show. Ellen Ratner of the Talk Radio News Service provides Washington commentary daily.

When callers to the show ask him how he is, he usually replies, "I'm great, but I'll get better," and he ends each show with the phrase, "Activism begins with you, Democracy begins with you, get out there, get active! Tag, you're it!"

TV program

Hartmann produces a half-hour daily TV show, "The Big Picture," which is syndicated by Free Speech TV and carried on both Dish Network satellite TV channel 9415 and on a wide variety of local cable TV stations from WSCS in Cheboygan, Michigan, to DUTV in Philadelphia, to Portland Community Media (Comcast) in Portland, Oregon.

Hartmann began his business career in in the early 1970s while in his 20s, co-founding The Woodley Herber Company. Woodley Herber sold herbal products, potpourris and teas, and operated until 1978. It was during this time that Hartmann obtained three degrees in herbology and homeopathic medicine, one of which was from a diploma mill. Thereafter Hartmann moved to New Hampshire to begin The New England Salem Children's Village, which still operates in Rumney, New Hampshire. He was Executive Director of NESCT for five years, and on its board for over 25 years. NESCT's child-care model was based on that of the German Salem International organization, and through his affiliation with that group he helped start international relief programs in Uganda, Colombia, Russia, Israel, India, Australia, and several other countries between 1979 and today.

Hartmann founded International Wholesale Travel and its retail subsidiary Sprayberry Travel in Atlanta in 1983, a business which in the intervening years has generated over a quarter of a billion dollars in revenue. According to their website, Sprayberry Travel was lauded by the Wall Street Journal in 1984 for being one of the early adopters of frequent travel programs analogous to the recently initiated frequent flyer programs of the airline industry. He sold his share in the business in 1986 and retired with his family to Germany to work with the international relief organization Salem International. In the late 1970s, he had been a trainer in advertising and marketing for The American Marketing Centers (now defunct), and in 1987 after returning from Germany founded the Atlanta advertising agency Chandler, MacDonald, Stout, Schneiderman & Poe, Inc., which did business as The Newsletter Factory. He sold his interest in that company in 1996 and retired to Vermont.

Hartmann is a writer who has published more than twenty books on diverse topics. The title which won the most critical acclaim is The Last Hours of Ancient Sunlight. In 1999 he was invited by the Dalai Lama to spend a week in Dharamsala after the Dalai Lama finished reading this book. Hartmann won the Project Censored Award in 2004 for Unequal Protection. As a result of a book on spirituality, The Prophet's Way, he was invited in 1998 to meet Pope John Paul II.

Trained in the 1970s in Neuro-Linguistic Programming by Richard Bandler (Hartmann is licensed by Bandler's Society of NLP as both an NLP Practitioner and an NLP Trainer, and Bandler wrote the foreword to his book "Healing ADD"), Hartmann popularized some of its concepts in Cracking the Code (2007), which argues that Newt Gingrich and Frank Luntz made use of them in the 1980s and 1990s for Republican Party causes and advocates using them to advance liberalism. His book "Healing ADD" also leans heavily on NLP techniques. His book on the JFK Assassination (written with Lamar Waldron) titled "Ultimate Sacrifice" is cited extensively in the last two chapters of Gore Vidal's recent autobiography as having "finally solved" that case.

Hartmann was one of several contributors to Air America, the Playbook, A 300 plus page collection of essays, transcripts, and interviews by liberal radio personalities. It was published shortly before the 2006 Congressional elections and was on the New York Times Best Seller list for October 8, 2006.

Leonardo DiCaprio made a web movie titled "Global Warning" that was inspired by The Last Hours of Ancient Sunlight. Hartmann appears in DiCaprio's 2007 documentary The 11th Hour, as well as the feature documentary film Dalai Lama Renaissance (with Harrison Ford), and Crude Impact.

Hartmann has authored in the area of attention-deficit hyperactivity disorder (ADHD) and adult attention-deficit disorder (AADD) and is the creator (first proposed by him in 1978, first published nationally in 1992) of the now well-known hunter vs. farmer theory that ADD is an expected evolutionary adaptation to hunting lifestyles. These individuals have the ability of rapidly shifting their focus and external attention and of holding multiple trains of thought. This ability causes difficulties when they must live and work in cultures in which "farming" — well-planned, predictable, organized and repetitive behaviours — is typical. His first book on the disorder, Attention Deficit Disorder: a Different Perception was described by Scientific American as "innovative and fresh". Hartmann has established specialized schools for children with ADHD, such as The Hunter School in Rumney, New Hampshire, which he cofounded with his wife Louise.