[4] He has regularly appeared as Dr. Peter Lindstrom on Law & Order: Special Victims Unit, and had a recurring role as "The Dick & Jane Killer" on CSI: Crime Scene Investigation.

Irwin has created several highly regarded stage shows that incorporate elements of clowning, often in collaboration with composer Doug Skinner.

These works included The Regard of Flight (1982), which ran on Broadway at the Vivian Beaumont Theatre in April 1987 for 17 performances,[9] Largely New York (1989), Fool Moon (1993),[10] The Harlequin Studies (2003),[11] and Mr. Fox: A Rumination (2004).

In 2013, he teamed with his occasional partner David Shiner to create and perform in the Off-Broadway "clowning revue-with-music" Old Hats along with actress and musician Nellie McKay.

Irwin performed with The Cadets Drum and Bugle Corps at the 1996 Summer Olympics, in a "band on the run" sequence where he played Dr. Hubert Peterson of the fictitious Federation of United Marching Associations of America.

Irwin appeared with Steve Martin and Robin Williams in the Lincoln Center Off-Broadway production of Waiting for Godot, in 1988, in the role of Lucky.

[20] In 2005, he starred as George alongside Kathleen Turner in a revival of Edward Albee's Who's Afraid of Virginia Woolf?, for which he won a Tony Award.

[24] Irwin's first featured film role was in 1980, appearing as Harold Hamgravy in Robert Altman's Popeye starring Robin Williams.

Irwin's principal film roles include playing Eddie Collins in Eight Men Out, which tells the story of the "Black Sox" gambling scandal of 1919, and My Blue Heaven, a 1990 comedy with Steve Martin and Rick Moranis.

Irwin tap-danced in a leading role in 1991's Stepping Out with Liza Minnelli, appeared as a mime in the Paul Mazursky film Scenes from a Mall alongside Woody Allen and Bette Midler, and played Charlie Sheen's father in Hot Shots!

In 2006, Irwin played the solitary Mr. Leeds in M. Night Shyamalan's Lady in the Water and had a small role as Uncle Teddy in 2007's Across the Universe.

He received critical acclaim for his role as Paul, father to Anne Hathaway's character Kym, in the 2008 drama Rachel Getting Married.

He is featured in the PBS series Great Performances, in the episode titled "Bill Irwin, Clown Prince", initially broadcast in December 2004.

[citation needed] In 2000, the Jazz Tap Ensemble in Los Angeles received a $10,000 grant from the National Endowment for the Arts (NEA) "for a commission of a new work by Bill Irwin.