Armstrong also previously played for the Atlanta Thrashers, Toronto Maple Leafs and Montreal Canadiens.

The Penguins and Armstrong avoided an arbitration hearing in the 2006–07 off-season by re-signing him to two-year, $2.2 million contract.

[16] On July 1, 2010, Armstrong signed as an unrestricted free agent with the Toronto Maple Leafs on a three-year, $9 million contract.

[18] With the opening of free agency the next day, July 1, 2012, Armstrong signed a one-year, $1 million contract with the Montreal Canadiens.

[10] After the season resumed, Armstrong suffered another major injury in an April game versus the Carolina Hurricanes.

[21] On July 27, 2013, Armstrong left the NHL as a free agent and signed his only European contract with the Växjö Lakers of the Swedish Hockey League, playing one season.

[23] He also played in the 2009 IIHF World Championship for Team Canada[24] where they won the silver medal after losing to Russia 2–1 in the final.

[25] Rogers Media hired Armstrong as an analyst for Sportsnet's national coverage of the NHL starting in the 2014–15 season.

[29] Armstrong's younger brother Riley briefly played in the NHL with the San Jose Sharks.