He received a writing credit for National Lampoon's Lemmings which helped launch the careers of John Belushi, Chevy Chase, and Christopher Guest. He also co-wrote National Lampoon's 1964 High School Yearbook with Douglas Kenney. O'Rourke said later that Kenney brought comedy to the piece and he brought the organization. The Yearbook was a bestseller and some themes were later used in the movie Animal House.

O'Rourke was born in Toledo, Ohio, the son of Delphine (née Loy), a housewife, and Clifford Bronson O'Rourke, a car salesman. He received his undergraduate degree from Miami University in 1969 and earned an M.A. in English at Johns Hopkins University (where he was a brother of the Alpha Delta Phi Fraternity) in 1970. He claims that during his student days he was a left-leaning hippie, but that in the 1970s his political views underwent a volte-face. He emerged as a political observer and humorist rooted in libertarian conservatism.

O'Rourke wrote articles for several publications, including "A.J. at N.Y.U." for The Rip Off Review of Western Culture, an underground magazine/comic book, in 1972, as well as pieces for the Baltimore underground newspaper Harry and the New York Ace, before joining National Lampoon in 1973, where he served as editor-in-chief, among other roles, and authored articles such as "Foreigners Around the World" and "How to Drive Fast on Drugs While Getting Your Wing-Wang Squeezed and Not Spill Your Drink."

O'Rourke was a proponent of Gonzo journalism; one of his earliest and best-regarded pieces was "How to Drive Fast on Drugs While Getting Your Wing-Wang Squeezed and Not Spill Your Drink", a National Lampoon article in March 1979. The article was republished in two of his books, Republican Party Reptile (1987) and Driving Like Crazy (2009).

Going freelance in 1981, O'Rourke began publishing in magazines such as Playboy, Vanity Fair, Car and Driver, and Rolling Stone. He became foreign-affairs desk chief at Rolling Stone, where he remained until 2001. In 1996, he served as the conservative commentator in the point-counterpoint segment of 60 Minutes. During the Bosnian genocide, O'Rourke received criticism for using the American public's lack of interest in Bosnia as a way to joke about "unspellables killing the unpronouncables."

O'Rourke was married to Amy Lumet, a daughter of movie Director Sidney Lumet and a granddaughter of Lena Horne, from 1990-93. Since 1995 he has been married to his second wife, Tina; they have two daughters, Elizabeth and Olivia, and one son, Clifford. In an interview with The New Statesman, O'Rourke revealed that his "wife is a Catholic, the kids are Catholic" and described himself as, therefore, a "Catholic fellow-traveller". The family divides their time between Sharon, New Hampshire and Washington, D.C.

The Forbes Media Guide Five Hundred, 1994 states:

O'Rourke types his manuscripts on an IBM Selectric typewriter, though he denies that he is a Luddite, asserting that his short attention span would make focusing on writing on a computer difficult. In a January 2007 interview, O'Rourke gave an Example of his view of computers and writing by referencing Novelist Stephen King, whom he paraphrased – saying had he a computer, he could have written three times as much in his early days. To which O'Rourke remarked, "Does the world need three times as many Cujos? Three times as many Jane Austens, maybe."

O'Rourke revealed on September 28, 2008, that he had been diagnosed with treatable anal cancer, from which he expected "a 95% chance of survival."

In 2009, O'Rourke described the presidency of Barack Obama as "the Carter administration in better sweaters". However, in 2016, he endorsed presidential candidate Hillary Clinton over Donald Trump. O'Rourke stated that his endorsement included her "lies and empty promises," and said, "She's wrong about absolutely everything, but she's wrong within normal parameters."