The Boro skipper had missed the club's last two matches because of a clause in his contract that meant the Teessiders were due £1m to Portsmouth if he made his 100th appearance in a Boro shirt.
Boro chief executive Keith Lamb has spent the last week negotiating with the administrator currently running Portsmouth FC, and a pay-as-you-play agreement has been struck that will allow the midfielder to play in Boro's final three games of the season.
He returns to the starting line-up this evening in place of Jonathan Franks.
There is no place for David Wheater though, and the defender is unlikely to play again this season after damaging his ankle ligaments in training yesterday.
Wheater is replaced by Jonathan Grounds as Boro look to secure the victory they need to keep their play-off hopes alive.
WEST BROM (4-4-2): Carson; Reid, Tamas, Olsson, Cech; Brunt, Dorrans, Mulumbu, Koren; Cox, Bednar.
Subs: Kiely (gk), Mattock, Miller, Barnes, Meite, Morrison, Slory.
MIDDLESBROUGH (4-4-2): Jones; Hoyte, McManus, Grounds, Naughton; Robson, O'Neil, R Williams, Arca; McDonald, Killen.
Subs: Coyne (gk), Taylor, Riggott, Lita, O'Shea, Miller, Franks.