Hargrove, who signed for the veteran minimum salary benefit of $840,000 and counts $555,000 against the cap, missed the 2012 season after serving an eight-game suspension for his role in the New Orleans Saints bounty scandal.
Hargrove had signed a deal with the Green Bay Packers but was released in August. After his suspension, no other team signed him.
Hargrove, 29, has played with four NFL teams and last played a full season with the Seattle Seahawks in 2011. That season, Hargrove compiled three sacks and 13 total tackles in 15 games.
Since being drafted by the St. Louis Rams in 2004, Hargrove has started 25 games and has 19.5 sacks, three forced fumbles and five fumble recoveries. He was suspended for the 2008 season for violating the league's substance-abuse policy.
Hargrove brings depth to the Cowboys' defensive line at some of the inside positions. The Cowboys have told Tyrone Crawford, who enters his second season, he will play both tackle and end in 2013.
To make room on the roster, the Cowboys released guard D.J. Hall.