Moulson grew up in Mississauga, Ontario, playing minor hockey for A Erindale, AA York Toros, AAA North York canadiens, AAA Mississauga Senators, AAA Markham Islanders, AAA Mississauga Reps and at Midget for the AA Mississauga Braves of the GTHL.
After his midget days, Moulson signed with the Guelph Dominators Junior B club of the Midwestern Ontario Junior B League (OHA) for the 2000-2001 and 2001-02 seasons. The following four years, Moulson attended Cornell University.
Moulson was drafted 263rd overall by the Pittsburgh Penguins in the 2003 NHL Entry Draft. Moulson attended Our Lady of Mount Carmel Secondary School in Mississauga, where he was a part of the school’s hockey team. Moulson graduated from Cornell University in 2006, where he was captain of the hockey team and a member of the Quill and Dagger society in his senior year.
He signed with the Los Angeles Kings as a free agent to an entry-level contract on September 1, 2006. He was then assigned to the Kings affiliate, the Manchester Monarchs of the AHL for the 2006–07 season, scoring 57 points in 77 games. Moulson made his NHL debut in the 2007–08 season on November 2, 2007, against the San Jose Sharks. Moulson also scored his first NHL goal in the 5-2 victory.
On July 6, 2009, Moulson signed a one-year contract with the New York Islanders. Moulson was a leading scorer in preseason and made the team out of camp as a linemate of John Tavares. He scored his first NHL hat trick—a natural hat trick—on December 3, 2009, against the Atlanta Thrashers.
After the 2011-2012 NHL Season, Moulson became the first New York Islander since Zigmund Palffy to post three consecutive 30 goal seasons.
Moulson married Alicia Backman on July 3, 2010. Alicia’s sister, Jaclyn, is the wife of Los Angeles Kings goaltender Jonathan Quick. His sister, Shannon Moulson played her NCAA hockey for the Niagara Purple Eagles women’s ice hockey program and currently competes in the Canadian Women’s Hockey League for the Burlington Barracudas.