The 24-year-old had 34 points (12-22) in 80 games last season. Three of his goals were scored in overtime. "Colby is another young guy who plays with passion, gives us versatility up front and brings an added physical dimension to our team," said GM Ray Shero. "We are confident he'll continue to grow as a player."
Armstrong helped Canada capture a gold medal at the IIHF World Hockey Championship in Moscow this past May. He scored a goal in the final game.
The native of Lloydminster, Sask., has 74 points (28-46) in 127 NHL games - all with Pittsburgh. He was drafted 21st overall by the Penguins in 2001.
The Penguins also signed minor-leaguers Chris Minard, a centre from Owen Sound, Ont., and Nathan Smith, a centre from Strathcona, Alta., to two-year contracts.
Minard, 25, led the AHL's Lowell Devils with 49 points (32 goals, 17 assists) last season.
Smith, 25, earned 40 points (19-21) in 72 games with the AHL's Manitoba Moose, and he played one game for the Vancouver Canucks.