Carter, a regular at the Pro Bowl during his many years with the Minnesota Vikings, reportedly agreed to terms with the Dolphins over the weekend.
The Dolphins had talked to Carter in the offseason but couldn't reach a contract agreement and Carter decided to take a job with HBO's "Inside The NFL."
Carter's contract with HBO included an out clause allowing to leave to play again.
The Dolphins renewed talks with Carter last week after Oronde Gadsden sustained a significant wrist injury in the Sunday night victory over Denver.
Gadsden apparently has decided to go ahead and have surgery next week, which will knock him out for the remainder of the season.
Gadsden is scheduled to become an unrestricted free agent after the season, and that complicated his situation. His agent approached the Dolphins about giving Gadsden a contract extension right now, but the two sides couldn't agree on a new deal.