McColgan was born in the Savin Hill area of Dorchester, Massachusetts, and attended Catholic Memorial High School in West Roxbury, Massachusetts. His interest in music began while he sang in the school's choir. McColgan joined the U.S. Army in 1989 and served in an Army artillery unit in the first Gulf war before becoming a founding member of the Dropkick Murphys in 1996. While McColgan was with the Murphys, they released one full-length album, Do or Die.
According to McColgan, he always wanted to be a member of the Boston Fire Department like his uncle and role-model, Kevin O'Toole (the subject of "Kevin J. O'Toole" on State of Grace). When McColgan left the band in 1998 to pursue this dream he was replaced as lead singer by Al Barr, ex-vocalist for The Bruisers. Regarding his 1998 departure, McColgan said "I have no misgivings, no regrets…and there are no bad feelings...I still talk to those guys." The song "Two Angry Kids" on State of Grace is reportedly a reminiscing of the times spent with Dropkick Murphys frontman Ken Casey.
McColgan, however, after a few years started a new band known as the Street Dogs and shortly left the fire department to again pursue music fulltime. The Street Dogs featured members such as Johnny Rioux and Joe Sirois (of the Mighty Mighty Bosstones). Guitarist Marcus Hollar sent McColgan an e-mail saying that if his new band ever needed a guitarist, that he was available. McColgan gave Hollar an audition and asked him to join the band.
The Street Dogs have toured with Social Distortion, Flogging Molly, Tiger Army, The Bouncing Souls, The Adolescents, The Offspring, The Bones, The Swingin' Utters, and Anti-Flag. They have also appeared on Warped Tour and had a successful headlining tour at the end of 2005. The band's third album, Fading American Dream, was released October 24, 2006. In support of the album, the band went out on The Gold Tour from October through December with The Bouncing Souls. In February 2008, it was announced that the Street Dogs signed on to Hellcat Records and the band released their fourth album, State of Grace, on July 8, 2008. The Street Dogs released their fifth studio album, Street Dogs on August 31, 2010.
- Oi!/Skampilation 3. (1997) (Produced By Derek TC NYSR)
- Boys on the Docks EP (1997)
- Do or Die (1998)
- The Singles Collection, Volume 1 (2000, contains material released before Do or Die)
- Savin Hill (2003)
- Street Dogs/The Dents Split (2004)
- Tales of Mass Deception EP (2004)
- Back to the World (2005)
- Fading American Dream (2006)
- State of Grace (2008)
- Street Dogs (2010)
The Bones (Sweden)
- Featured in: "Yesterday's Heros" - Partners In Crime Vol. 1 (2006)