He is best known for his roles as Dr. Sean McNamara on the FX television series Nip/Tuck,[1] Al Burns on Unforgettable, and Sam Lane on Superman & Lois.

[6] His family returned to the United States when he was ten years old and settled in Virginia, where Walsh began acting in high school.

He continued to work in films including Betsy's Wedding, Nobody's Fool, Congo, The Stepfather, and Secretariat and guest starred the television series Brooklyn South, The Twilight Zone, and Everwood.

Walsh starred as Lieutenant Al Burns in all four seasons of CBS's crime-drama series Unforgettable, which ran from 2011 to 2016.

[8][9] Walsh met Leslie Bourque and had a daughter, Amelie Belle,[8] and a son, Hudson Scott.