Armstrong, 30, had two goals and five points in 37 games with the Canadiens in 2012-13, his eighth season in the NHL.
He was the Pittsburgh Penguins' first-round pick (No. 21) in the 2001 NHL Draft and made his debut with the Penguins in 2005-06, scoring 16 goals and finishing with 40 points in 47 games. The Penguins traded him to the Atlanta Thrashers in February 2008, and he had a career-best 22 goals for the Thrashers in 2008-09.
He signed a three-year contract with the Toronto Maple Leafs in the summer of 2010, but was bought out last summer and signed with the Canadiens. In 476 NHL games, Armstrong has 89 goals, 209 points and 376 penalty minutes.