Carter announced on his Twitter account that he was joining the Patriots, and a league source confirmed the sides have an agreement.
The 32-year-old Carter enters his 11th NFL season, having played for the San Francisco 49ers (2001-2005) and Washington Redskins (2006-2010). He has appeared in 149 career regular-season games (133 starts), totaling 66 career sacks.
The Patriots signed speed rusher Mark Anderson (Bears/Texans) on Friday and reached a contract agreement with versatile defensive lineman Shaun Ellis (Jets), pending a physical, earlier on Sunday. Now the 6-foot-4, 257-pound Carter joins the mix and his arrival could signal a shift away from the team's 3-4 alignment. Carter is considered a more natural fit in a 4-3 defense.
Meanwhile, the defense has looked a bit thin at end, where six-year veteran Eric Moore and 2010 second-round draft choice Jermaine Cunningham have lined up. With Carter set to come aboard, along with Anderson and Ellis, the Patriots now have more options at the position.
Mike Reiss covers the Patriots for ESPNBoston.com.