Herlihy was born in Brooklyn, New York, and raised in Poughkeepsie, New York. His father was a New York City firefighter. He graduated from Arlington High School in 1984.
After graduating in 1988, Herlihy spent a year as an accountant at Ernst & Young in Manhattan before returning to NYU for law school. While a student there, Herlihy collaborated with Sandler (who had recently been hired at Saturday Night Live) on sketches, including Cajun Man. After law school, Herlihy worked as a securities Lawyer at Cahill Gordon & Reindel in lower Manhattan.
Herlihy has written for and/or performed on three of Sandler's comedy albums: They're All Gonna Laugh at You! (1993), What the Hell Happened to Me? (1996) (both 2x Platinum) and Shhh...Don't Tell (2004).
Herlihy was hired as a Writer at Saturday Night Live in March 1994. He remained at the show after Sandler left in 1995, rising to head Writer and eventually Producer. He wrote many political sketches leading up to the 1996 Presidential election, and co-wrote (with Tina Fey) the 1999 Sketch in which Monica Lewinsky appeared. He left the show in 1999 to focus on film work.
He is best known for writing or co-writing the Sandler films Billy Madison (1995), Happy Gilmore (1996), The Wedding Singer (1998), The Waterboy (1998), Big Daddy (1999) and Pixels (2015).
Herlihy played a bartender in both The Wedding Singer (1998) and The Ridiculous 6 (2015).
In 2006, Herlihy co-wrote the book and two songs for a Broadway musical version of his film The Wedding Singer. It opened at the Al Hirschfeld Theatre on April 27, 2006 and closed on December 31, 2006 after 284 performances. Herlihy and Chad Beguelin's book was nominated for the 2006 Tony Award for Best Book of a Musical, and the show itself was nominated for the Tony Award for Best Musical. It subsequently has had many international productions.
Herlihy returned to Saturday Night Live for one episode in 2015, to work with Tracy Morgan on a recurring Sketch they had created in the 90's, Brian Fellow's Safari Planet. That episode was nominated for an Emmy Award for outstanding writing, and won a Writers Guild Award for Outstanding Writing for a Comedy/Variety Sketch series.
In 2015, Herlihy co-wrote (with Sandler) the Western comedy film The Ridiculous 6, distributed by Netflix. Despite being universally panned by critics, on January 6, 2016, it was announced by Netflix that the film had been viewed more times in 30 days than any other movie in Netflix history.
