Irwin played in the National Hockey League (NHL) for the San Jose Sharks, Boston Bruins, Nashville Predators, Anaheim Ducks, Buffalo Sabres and the Washington Capitals.

He was named best defenceman in the British Columbia Hockey League Coastal Conference two years in a row, 2007 and 2008, while playing for the Nanaimo Clippers.

[2] Irwin scored 73 points in his first two seasons, and was signed by parent affiliate, the San Jose Sharks after injuries to Jason Demers and Brent Burns.

As a free agent from the Ducks, Irwin agreed to a one-year, $700,000 contract to join his fifth NHL club in the Buffalo Sabres on October 9, 2020.

Irwin continued his journeyman career in the following off-season, leaving the Sabres to sign as a free agent on a one-year, two-way contract with the Washington Capitals on July 28, 2021.