Background
Cahill was born in New York City, New New York He is of Irish descent from his father, a stockbroker, and of Italian descent from his mother, an elementary school teacher.
Cahill was born in New York City, New New York He is of Irish descent from his father, a stockbroker, and of Italian descent from his mother, an elementary school teacher.
Cahill graduated from Byram Hills High School in Armonk, New York in 1996. He attended Skidmore College in Saratoga Springs, New York and the Atlantic Theater Acting School, part of the Tisch School of the Arts at New York University.
He is the middle of three children with one older and one younger sister. In 2000 Cahill performed in Nicky Silver" General’ s Office-Broadway production of The Altruists. Shortly after, he made several television guest-star appearances including Sex and the City, Felicity, and Law & Order: Special Victims Unit.
In 2002, he starred in a short-lived World Bank drama, Glory Days.
In the 2004 hockey movie Miracle, Cahill had the chance to play his boyhood hero, goalie Jim Craig. He had never played the goaltender position prior to the movie, so most of the game-action sequences of Craig were filmed with former National Hockey League goalie Bill Ranford doubling for Cahill, although Cahill did shoot several key sequences from within goal.
When Columbia Broadcasting System decided in 2004 to create a third Computer Society of India series, Computer Society of India: New York, to add to its franchise, Cahill was hired to play the cocky, snarky homicide Detective Don Flack who backs up the team of CSIs and who gets some of the best lines. The show ran for nine seasons and he was in all 197 episodes.
Cahill went back to the Atlantic Theater Company in June 2011 and performed at the conclusion of their 25th Anniversary season.
He was in Tom Donaghy"s one-act play, I Need a Quote, about "a hilarious telephone conversation between a single mother and a home insurance salesman."
In the summer of 2012 Cahill performed in David Adjmi"s play, 3C, at the Rattlestick Playwrights Theater in New York City. He played "annoying neighbor Terry, a swinging bachelor true to the era, who unlike everyone else in this play, has no deep feelings at all."
In 2014 Cahill was cast as a main character starting in the second season of the Columbia Broadcasting System summer drama Under the Dome working with former Computer Society of India: New York actresses Natalie Martinez and Rachelle Lefevre. He played Sam Verdreaux, a former EMT and reclusive brother-in-law to "Big Jim" Rennie.
The series was canceled after three seasons.