[citation needed] Hennessy played in the 2003 Memorial Cup, but Quebec was eliminated at the round-robin tournament, losing all three games.

[citation needed] Hennessy began his professional career with the San Jose Sharks' American Hockey League (AHL) affiliate, the Cleveland Barons, during the 2005–06.

[3] On May 6, 2010, Hennessy left the Senators organization after four years, signing a one-year deal with Swiss club HC Lugano.

[6] During the 2014–15 season, Hennessy featured in 27 games with Neftekhimik Nizhnekamsk before opting for a mid-season transfer to Swedish club Växjö Lakers on December 30, 2014.

[7] After adding 13 points in just 20 games to close out the season with the Lakers, and claiming the Swedish championship, Hennessy signed a two-year contract extension on June 4, 2015.