Career
Leahy originally played hockey at Boston College High School of the Catholic High School Conference. During his time at British Columbia High, Leahy set a school record for points in career (with 140), was named to the Boston Globe and Boston Herald Dream Teams as a senior, and was honored with the titles of team captain and Most Valuable Player. After being drafted in the 5th round, 122nd overall, at the 1998 National Hockey League Entry Draft by the New York Rangers, Leahy spent 4 years playing college hockey for Miami University in Oxford, Ohio before he turned pro in 2001. During his first year of professional hockey, Leahy played for four pro teams, including the Trenton Titans of the ECHL, the Hershey Bears, the Portland Pirates and the Bridgeport Sound Tigers of the American Hockey League.
After bouncing around during the 2001-2002 season, Leahy settled with the Providence Bruins for the entire 2002-2003 season before signing with National Hockey League affiliate, the Boston Bruins the following season on July 28, 2003.
During the 2003-2004, Leahy made his National Hockey League debut with the Bruins against the Philadelphia Flyers on December 6, 2003. After 6 scoreless games with Boston he was returned to the P-Bruins.
Remaining with Providence through the 2004 National Hockey League Lockout, Pat made the Bruins opening roster for the 2005-2006 season and on October 8, 2005, he scored his first National Hockey League goal (unassisted) against the Pittsburgh Penguins. In 43 games with Boston he scored 4 goals for 8 points before reassigned to Providence.
On July 17, 2006, Leahy left the Bruins organization and signed a one-year contract as a free agent with the Nashville Predators.
Making just a single appearance with the Predators during the 2006-2007 season, Leahy was assigned to AHL affiliate, the Milwaukee Admirals of the majority of the year. Unable to establish a National Hockey League spot after six professional seasons, Leahy signed with European team EHC Black Wings Linz of the Austrian Hockey League. Leahy spent the last 7 seasons of his career with Linz, culminating with a Championship in 2012 before retiring at the end of the 2013-2014 season.