Allen, a 6-foot-5, 328-pound defensive tackle out of Louisiana State, joins the Packers from the New York Giants, where he spent the previous two seasons.
Allen played in 14 total games last year, mainly as a reserve. He finished with 21 tackles (15 solo), two sacks and two fumble recoveries. In a game at Philadelphia on Dec. 11, he recovered a Mike McMahon fumble in overtime to give New York possession on the Eagles' 27-yard line, setting up the game-winning field goal.
Allen, who made the New Orleans Saints as an undrafted free agent in 2003, has played in 29 games overall with three starts. He has 51 tackles (40 solo), three sacks and a pair of fumble recoveries.
Allen joined the Giants on waivers in 2004.