Shaw made his big money move to Old Trafford during the World Cup this summer, where he will have learned many lessons with the England squad who were hugely disappointing.
The Southampton youngster is set to be first choice at United this season despite not technically being a Louis van Gaal signing, although the new boss did approve the deal while also in Brazil.
Irwin is pleased that the Red Devils are looking at youth this summer and believes Shaw will be an instant success.
“He is going to be a fantastic signing for years to come,” Irwin said.
“He showed he has great pace for England at the World Cup and in the warm-up games. He has always been great going forward, we have seen that in the Premier League.
“There was talk of Chelsea being in for him so I am delighted that he signed for United.”