In 1987, Saturday Night Live’s executive producer hired O’Brien as a writer of many famous sketches; like many SNL writers, he occasionally appeared as an extra in the sketches: his most notable appearance was as a doorman in a sketch in which Tom Hanks was introduced into SNL for hosting his fifth episode. In 1989, O’Brien and his fellow SNL writers received an Emmy Award for Outstanding Writing in a comedy or variety series. He worked for the show until 1991.
From 1991 to 1993, O’Brien was a writer and a producer for The Simpsons.
From 1993 to 2009, he hosted the American late night show on NBC. He left the direction in 2009 to succeed Jay Leno as the host of The Tonight Show. The show was known for its absurd comedic sensibility and for its sarcasm and irony.
In 2004, O’Brien negotiated a new contract with NBC: he took over the Tonight Show from Jay Leno in 2009.