After graduating from Hobart College with a major in English, Lax joined the Peace Corps serving in Truk and the Caroline Islands in the Western Pacific. After completing his two year placement, he worked in Washington D.C., first as a Peace Corps Fellow, then as Overseas Director of the Peace Corps School Partnership Program, which allowed him to travel to 43 countries.
He left the Peace Corps in 1970 to pursue writing full-time. Lax's longtime passion for comedy resulted in his first book, On Being Funny (1975), in which he used the work and thoughts of Woody Allen as a means of writing about comedy in general. In 1984, Lax authored Life and Death on 10 West, about the bone marrow transplantation ward at the UCLA Medical Center, which was headed at the time by classmate Dr. Robert Peter Gale '66. His work was recognized by the New York Times Book Review as one of the Notable Books of the Year and received an award from the American Leukemia Society.
In 1991, Lax published the best seller and New York Times Notable Book of the Year, Woody Allen: A Biography, which was translated into 17 languages. Five years later, Lax wrote Paul Newman: A Celebration, followed in 1997 by Bogart, co-authored with A.M. Sperber. His most recent book - The Mold in Dr. Florey's Coat, about the development of penicillin – was published in 2003.
Lax has contributed to many magazines, including Atlantic, Life, The Washington Monthly, the New York Times Magazine, The New Yorker, Vanity Fair and Esquire, where he was a contributing editor. He is a board member and past president of PEN Center USA West, a member of the International PEN Board, and chair of the trustees of the International PEN Foundation.