Byrne was exposed to stand up comedy while working at the comedy club Caroline's in New York City. The first time he got on stage was at Stand Up New York on September 30, 1997.

In 2003, Byrne filmed the documentary film 13 or Bust, where he did 13 shows in one night at every comedy club in Manhattan, breaking the record for most sets in one night by a comedian. His Comedy Central Presents Half Hour Special premiered in 2006 and was voted the seventeenth-most-popular Comedy Central Presents by fans as part of the Standup Showdown on comedycentral.com. That same year, he did a show for Comedy Central and the troops at Ft. Irwin in 2006. Byrne has participated in USO tours of Afghanistan in June 2008, Japan and Guam in July 2009 and Afghanistan again in 2010.

He has had small parts in several films: The Goods: Live Hard, Sell Hard, starring Jeremy Piven and produced by Will Ferrell; Four Christmases, starring Vince Vaughn and Reese Witherspoon; and Couples Retreat, starring Vince Vaughn and Jon Favreau.

Byrne had a one-hour special on Comedy Central in 2008 titled Steve Byrne's Happy Hour. In 2010, he had another one-hour special on Comedy Central titled The Byrne Identity. He filmed his third hour special Feb. 8th in New York City in 2014, called Champion, for Netflix.