The veteran spent the 2011 season with the Patriots, recording 10 sacks before being placed on injured reserve due to a quadriceps injury.
After spending the 2012 season with Oakland, Carter remained unsigned up to this point, though he did work out for the Patriots back on Sept. 9. He adds veteran leadership and a pass-rushing presence to a relatively young defensive line that has recently relied on a pair of rookie starters.
The Patriots have also added a big body along their defensive front, signing defensive tackle Sealver Siliga to their practice squad.
To make room for Siliga, the team released cornerback Travis Howard from the practice squad.
Siliga, who was shipped by the Broncos to the Seahawks earlier this season, is a 6-foot-2, 325-pound player who adds bulk and depth to the interior of the Patriots defensive line.
Originally an undrafted free agent for the 49ers back in 2011 out of Utah, Siliga was with the Broncos from 2011-13 before his brief tenure in Seattle, which included time on both the active roster and the practice squad.