Main Cast:
* Denis Leary as Tommy Gavin
* Daniel Sunjata as Franco Rivera
* Adam Goldberg as Mike Silletti
* Steven Pasquale as Sean Garrity
* Andrea Roth as Janet Gavin
* John Scurti as Chief Lou "Lou" DiSalvo
* Terry Kinney as Chief "Chief" Reilly
* Michael Lombardi as Black Shawn
* Jack McGee as Jimmy Keefe
Recurring Characters:
* Callie Thorne as Sheila "Shez" Keenan
* Melody "Mel" Sikes as Natalie Gavin
* Lauren Vélez as Carla "Carlie" Rivera
* Conleth Hill as Father "Father" O'Neill
* Diane Neal as Maggie Gavin
* Alicia Witt as Katie Gavin
Please note that this is not an exhaustive list, as there were many guest stars throughout the first season.