He was born in 1920 in Springfield, Massachusetts to Irish American parents. His father was a dentist, and he once said that his first "turn-on" was with nitric oxide from his father's office. At the age of 19, he upset his Catholic mother by dropping out of Holy Cross College, a Catholic college in Boston, two years before graduation. "The scholastic approach to religion didn't turn me on," he later said. He went on to West Point, but troubled his father, a retired American military officer, by leaving there too, this time after 18 months. He later claimed that his interests were "philosophic rather than militaristic".
Instead, he went to the University of Alabama where he graduated with a BA degree in Psychology in 1942. He enlisted as an Army psychologist, served in a Pennsylvania Hospital until the end of the Second World War, and got a PhD at the University of California at Berkeley. He became director of the Kaiser Foundation Hospital in Oakland and assistant professor at the University of California's School of Medicine in San Francisco (1950- 55).
According to one version of his life, Leary resigned his California jobs because came to believe that traditional psychiatric methods were harming some patients. According to another version, on the morning of his 35th birthday, his wife and the mother of their two children gassed herself in the garage - and that is why he resigned.
He took his children to Europe and, after returning, started working as a clinical lecturer at Harvard. There he evolved a theory of interpersonal behaviour in terms of games, even before Eric Berne's best-selling Games People Play (1961).
In 1960, then aged 39, beside the swimming pool of his rented summer villa in Cuernavaca, Mexico, he ate a handful of odd-looking mushrooms which he had bought from the witch doctor of a nearby village. Within minutes, he was later to recall, he felt himself "being swept over the edge of a sensory niagara into a maelstrom of transcendental visions and hallucinations. The next five hours could be described in many extravagant metaphors, but it was above all and without question the deepest religious experience of my life." On returning to Harvard he began experimenting on himself, his colleagues, and students with psilocybin, a chemical derivative of mushrooms with powerful mind-altering effects. He said he decided to "dedicate" the rest of his life to the "systematic exploration" of this "new instrument".
He and those around him started to experiment with other substances with similar mind-altering effects: morning-glory seeds, peyote, mescaline - and the most powerful substance of all - LSD-25. First sythesised in 1938 by Albert Hofmann, a Swiss biochemist, LSD in minute doses produces astonishing changes in perceptions, emotions and thoughts. Called both a psychotomimetic - that is a mimic of psychosis - and also a psychedelic - mind-revealing - drug, it was to transform the cultural life of the 1960s, especially among young people.
By 1963, Leary and LSD had become embarrassing for Harvard and they dismissed him and his younger colleague Dr Richard Alpert. Leary, Alpert and others organised a privately financed research group called the International Foundation for Internal Freedom (IFIF), and set up a psychedelic study centre in Zihuatenjejo, Mexico. However, anticipating adverse reactions, the Mexican government demanded that they leave the country.
A young New York millionaire, Billy Hitchcock, who believed that Leary's activities were important, turned over to him a 64-room house on a 4,000- acre estate in Millbrook, New York. There Leary established what he called the League for Spritual Discovery. He regarded himself as the founder of a new religion, and the mind-altering substances he used and advocated as "sacraments".
The Millbrook mansion, furnished and decorated like an Eastern temple, became Leary's headquarters, and a shrine and sanctuary for psychedelic migrants from all over the world. It also became a target for what Leary later called "the forces of middle-aged, middle-class" authority. A squad of police investigators headed by G. Gordon Lilly, later to achieve notoriety and a criminal conviction in the Watergate affair, arrested Leary and three other people at Millbrook for possession of marijuana.
A few months earlier customs officials in Laredo, Texas had searched Leary's car as he tried to enter Mexico, and had arrested him after finding a half-ounce of marijuana in the possession of his 18-year-old daughter. He alleged that the marijuana was for "scientific" work and also for "sacramental" use, as he was a practising Hindu. He was fined $30,000 and sentenced to 30 years in prison.
In 1970, helped by the Weathermen organisation and his third wife, he escaped from a California prison and eventually wound up in Algeria, where he took up residence-in-exile with black-power leader Eldridge Cleaver. In 1973 the USA Drug Enforcement Administration rearrested him in Kabul, Afganistan. He was extradited to the United States and imprisoned in California again. He got parole in 1976.
His gift for self-publicity is shown by his remark, aged 45, to Playboy magazine: "An enormous amount of energy from every fibre of your body is released under LSD - especially sexual energy. There is no question that LSD is the most powerful aphrodisiac ever discovered by man." At that time he said he had already taken LSD 311 times. He also told Playboy that he previously had been "a middle-aged man involved in the middle-aged process of dying", that his "joy in life", his "sensual openness", his "creativity" had all been "sliding downhill". Since then, thanks to psychedelic drugs, his life had "been renewed in almost every dimension . . . If you known a person's age, you know what he's going to think and feel about LSD. Psychedelic drugs are the medium of the young. As you move up the age scale - into the thirties, forties and fifties - fewer and fewer people are open to the possibilities that these chemicals offer."
The three inevitable goals of the LSD session are to discover and make love with God, to discover and make love with yourself, and to discover and make love with a woman. You can't make it with yourself unless you've made it with the timeless energy process around you, and you can't make it with a woman until you've made it with yourself.
In a 1968 book, The Politics of Ecstasy, he pronounced:
If you take the game of life seriously, if you take your nervous system seriously, if you take your sense organs seriously, if you take the energy process seriously, you must turn on, tune in, and drop out."
Most recently he was again in the news over the manner of dying. He had arranged with a cryonics organisation for his head to be frozen after his death, presumably with the idea that at some time in the future, technology permitting, his body would be reconstituted and "he" would be reanimated. However, afflicted with prostate cancer and near death, he changed his mind about cryonics. His very last plan was to go out in a blaze of publicity over the Internet.
Timothy Leary, psychologist and author: born Springfield, Massachusetts 22 October 1920; married five times (one son and one daughter deceased); died Los Angeles 31 May 1996.