Kings president of basketball operations Geoff Petrie announced the deal Monday, saying Armstrong would contribute immediately at power forward and center.
Armstrong is in his fourth NBA season out of Connecticut. He is averaging 2.8 points and 3.4 rebounds in 18 games this season. He has played 209 career games, averaging 3.6 points and 2.7 rebounds per contest.
Armstrong was the Big East defensive player of the year in 2006.