McWilliams was born to a Roman Catholic family and raised outside of Detroit in Allen Park, Michigan. After attending Eastern Michigan University, he read widely and was a fan of Paul Krassner's periodical The Realist and Albert Ellis' rational emotive therapy. After experimenting with yoga and LSD he also did group therapy with Melba Colgrove, Ph.D.

McWilliams began transcendental meditation with Maharishi Mahesh Yogi and wrote both The TM Book (by himself) and then later TM with Harold H. Bloomfield, M.D., leaving the TM organization shortly after introduction of its "TM-Sidhi Program." He was next active in Erhard Seminars Training with Werner Erhard whom he greatly admired and also Stuart Emory's "Actualizations" LGAT before meeting John-Roger Hinkins in the fall of 1978 and its "Insights" program.

He wrote nearly 40 books that he self-published under the names Versemonger Press and Prelude Press, including Surviving the Loss of a Love (1971), The Personal Computer Book (1982), The Word Processing Book (1982), Life 101: Everything We Wish We Had Learned About Life in School but Didn't (1990), and The Absurdity of Consensual Crimes in Our Free Society (1993). Many of these were liberally sprinkled with selected quotations to illuminate, often humorously, the points he made.

Life 101 and a few subsequent books were also credited to John-Roger (Roger Delano Hinkins), the leader of the Church of the Movement of Spiritual Inner Awareness and McWilliams's spiritual advisor during that time. McWilliams later repudiated the movement, claiming to be the sole author of the books, which clearly are written in his style.

All the books for which he holds copyright are available for reading at no charge at his web site. A notable exception is What to Do When Your Guru Sues You. McWilliams agreed to abandon the copyright to John-Roger to settle libel litigation over the contents of the book, and later asked that the book be removed from circulation in a notarized letter [1], stating "the content of the book is no longer one with which I would like to have my name associated".[2]

McWilliams was a budding photographer and a collection of his own photographs were published in October 1992. In the collection of photographs McWilliams is pictured with the family he writes about in Life 101. McWilliams photographs documents the Bohn families trip to "The Field of Dreams" in Dyersville Iowa in 1990.

In 1996, California Proposition 215 was approved by the voters that allowed terminally ill patients to use medical marijuana. The same year, Peter McWilliams was diagnosed with both cancer and AIDS and was among the roughly forty percent of terminally ill patients who experience extreme nausea as a side effect of medications used to treat such diseases. Advocates of medical marijuana (and many medical researchers) believe that the drug is an antiemetic, which eliminates the nausea associated with cancer and AIDS medications, thus allowing the medications to work effectively and enabling the patient to maintain their appetite and diet.

McWilliams became a strong supporter of medical marijuana and published Ain't Nobody's Business If You Do as a critic of victimless crime or consensual crime laws (to wit, as the premise of the book states, "any act which is a crime, which does not physically harm the person or property of another"; a stance shared by historical political philosopher John Stuart Mill), including the laws against marijuana. The book made him a hero among civil libertarians and critics of American drug prohibition. (The book's title is taken from the blues standard "Ain't Nobody's Business".)

McWilliams spoke before the Libertarian Party National Convention in 1998 where he came out as a gay man who was diagnosed with both cancer and AIDS and thus had a personal stake in the California law legalizing marijuana for medical reasons.

Along with the book Ain't, McWilliams was a vocal activist for medical marijuana and was helping Todd McCormick (who suffered from cancer since childhood) write a book titled How To Grow Medical Marijuana. Both men became the subject of a Federal Drug Enforcement Administration investigation; their homes were searched and research was seized to gather evidence towards charging both men with violating federal drug laws.

McWilliams claimed he was specifically targeted for arrest and prosecution because he was such an articulate and effective opponent of drug prohibition, as both Los Angeles County Sheriff's Deputies and DEA agents told him they frequently found copies of Ain't Nobody's Business... in the homes of those they arrested for marijuana possession. [3] [4]

McWilliams and McCormick were arrested and charged with violating federal drug laws concerning marijuana. The financial support that McWilliams gave to McCormick was used as evidence that he was a drug kingpin. At his trial, the judge ruled that McWilliams was not allowed to mention in court that he was terminally ill, that using medical marijuana was (in his opinion) keeping him alive, or that his usage of medical marijuana was legal under California state law. Even as he vomited repeatedly during court proceedings, McWilliams was, under such legal conditions, not allowed to explain his condition or its connection to the charges against him.

As a creative outlet and way to reach supporters during his trial, McWilliam's began to blog the current events of his life on his website petertrial.com. In his humorous, informative style, he shared his thoughts with the world, about his trial, medical condition and medical marijuana's effect on his life. Intro 0

Due to the gag restrictions, he was forced to plead guilty and hope that the judge would show leniency. Through his website letters, McWilliams asked supporters to send e-mails and letters to the presiding judge in an effort to allow McWilliams to serve his sentence under house arrest, where he could continue writing and have access to medical care. During this time, McWilliams continued writing articles highly critical of the laws against marijuana, including an open letter (published in Liberty magazine) to Microsoft founder and CEO Bill Gates which called on him to join the Libertarian Party.

ABC News reporter John Stossel had been a supporter of McWilliams' plight and had produced a Give Me A Break segment on Peter McWilliams a few days before McWilliams died in 2000. [5]

On June 14, 2000, McWilliams was found dead in his apartment. The New York Times reported that he had both AIDS and non-Hodgkin's lymphoma at the time of his death, but did not explicitly state that either disease directly caused his death. His mother's house had been used to collateralize the bond on which he was allowed to remain free pending sentencing, a condition of which was that he refrain from using cannabis. For fear of losing his mother's house, he did so, again forgoing the medication needed to control his symptoms. He had access to Marinol, but it was effective for him only one-third of the time. William F. Buckley Jr., a friend and an admirer, wrote a public letter expressing his grave concern that such a man should be made to die from excess vomiting under such uninformed conceptions of law (see below). [6]

The federal prosecutor personally called my mother to tell her that if I was found with even a trace of medical marijuana, her house would be taken away. [7]

Richard Cowan and many critics of the U. S. drug policies have described his death as murder by the U. S. government, insofar as they denied him the use of the medical marijuana which might have prevented his death. At least one account suggests that he choked on his own vomit because of the nausea [8] and William F. Buckley stated that he was vomiting when he died [9]. Others (including McWilliams himself, in Ain't) suggest those involved in such tragedies as his are otherwise good people whose dedication to the law had allowed them to be used for the purpose of enforcing unnecessarily cruel, unnecessarily expensive, and simply unnecessary laws, for the purpose of enforcing a morality that is in the interests of satisfying the moral offense of a segment of the American population, rather than satisfying the legitimate interests of America or Americans.

When his elderly mother pledged her house as security for the bail, they threatened that the government would seize her house if her son simply failed a drug test, not just if he were to flee. She would not be intimidated, but now her son is dead as the result of the conditions of the bail. These are the "family values" of America's war on the sick and dying. [10]

In October 2001, John Stossel reported again on McWilliams's story. The segment, entitled Sex, Drugs and Consenting Adults, included footage of the late author and was highly critical of victimless crime laws.