Sunderland have completed the signing of the 33-year-old on a permanent deal.
Sunderland have completed the signing of Grant Leadbitter on a permanent deal after he passed his medical on Monday.
As part of the deal, Leadbitter has agreed to take a pay cut to join the club in which he broke through the youth ranks in 2003.
Having fallen down the pecking order at the Riverside Stadium this season, and following the signing of John Obi Mikel, Tony Pulis has deemed Leadbitter surplus to requirements.
His high wages are likely to be another reason for Boro's willingness to let Leadbitter make the move to Sunderland, having been identified as one of four players the club would listen to offers for during the transfer window.
Leadbitter joined Boro in 2012 and has made 244 appearances for the club, most recently in the FA Cup fifth-round against Peterborough United. Boro manager Tony Pulis praised Leadbitter ahead of his move to Sunderland.
"He’s been absolutely fantastic since I’ve been at this football club," Pulis said. "I think he’s served the club brilliantly."
"He’s a Sunderland lad, and it’d be a wonderful move for him. Grant has a lot of affection for Sunderland, as he does with this club."