Kennedy played several years of his youth career with the Buffalo Regals, where he led the team with future Michigan State University teammate Chris Mueller.

On December 27, 2008, the Sabres called him up from Portland, giving him the opportunity to play his first NHL game in his hometown in Buffalo.

[4] On February 26, 2011, Kennedy was traded by the Rangers along with a third round pick to the Florida Panthers in exchange for Bryan McCabe.

On July 3, 2014, Kennedy continued his journeyman career by signing a one-year, two-way deal with the Washington Capitals, his original draft team.

On June 3, 2015, Kennedy signed a one-year contract with Russian club, HC Neftekhimik Nizhnekamsk of the Kontinental Hockey League (KHL) for the 2015–16 season.

[9] Kennedy described the experience in Nizhnekamsk as a poor fit for him; he was unable to adapt to the coaching regimen and the city's strict military environment, which prevented him from bringing his family to Russia, and partway through the 2015–16 KHL season, the club bought out his contract.

[11] On December 15, 2016, he parted ways with the club, due to a combination of injuries and the birth of his son back in the United States.