Carter signed a six-year, $30 million contract with the Washington Redskins as an unrestricted free agent on March 14, 2006. The Redskins moved Carter back to defensive end, his natural position. In his first year with the Redskins, he had 56 total tackles and six sacks. He showed much improvement in 2007, with 55 tackles, 10.5 sacks, and four forced fumbles. He also had a safety in a 34-3 win over the Detroit Lions. Carter's best season as a Redskin came in 2009 when he totaled 11 sacks. However, in 2010 the Redskins hired a new coach, Mike Shanahan, who changed their 4-3 defense to a 3-4 defense which required Carter to play outside linebacker. The Redskins released Carter on March 1, 2011.
Carter announced on his Twitter page on August 7 that he will be playing for the New England Patriots in 2011. It was later confirmed by Ian Rapoport of the Boston Herald and Michael Lombardi of the NFL Network. According to Rapoport, Carter signed a one-year deal with a base salary of $1.75m. He also received a $500k signing bonus and the chance to earn another $500k in incentives, making the contract worth up to $2.75 million. On November 13, 2011, Carter had a career game against the New York Jets, recording 4 sacks and tying the Patriots single game sack record. On Sunday, December 18, 2011 while playing against the Denver Broncos, Carter tore his left quadriceps tendon and missed the remainder of the 2011 regular season as well as the playoffs, as he underwent surgery. Despite being injured, Carter was one of eight Patriots honored by a selection to the 2012 Pro Bowl.
Carter is the son of former Denver Broncos defensive tackle Rubin Carter. He has a wife, Bethany, and two children: stepdaughter, Aysha, born in 1993, and a son, Quincy, born in 2007. His middle name was given to him by his father who named him after his close friend and co-player Andre Townsend.