He has gone straight onto the bench for this afternoon’s FA Cup third round tie against Manchester City.
Sir Alex Ferguson said: "It’s fantastic that Paul has made this decision. It’s always sad to see great players end their careers, but especially so when they do it early.
"But he has kept himself in great shape and I always felt that he had another season in him. It’s terrific to have him back."
Paul Scholes added: "I’ve been pretty clear since I stopped playing that I miss it. I’m delighted the manager feels I can still make a contribution to the team and I’m looking forward to playing my part in trying to bring more success to this great club.”