Nuno succeeds Graham Potter, who was dismissed this morning.
The Portuguese takes charge as a free agent after his axing by Nottingham Forest earlier this month.
Nuno has signed a three-year contract with the Hammers and will take charge of his first match on Monday evening when we travel to Everton in the Premier League.
“I am very pleased to be here and very proud to be representing West Ham United,” he said. “My objective is to work hard to get the very best from the team and ensure that we are as competitive as we possibly can be. The work has already started and I am looking forward to the challenge that is ahead.”
Nuno will be assisted in the interim by Academy coaches Mark Robson, Steve Potts, Gerard Prenderville and Billy Lepine, with a further announcement on his coaching and backroom staff to be made in due course.
He took his first training session as West Ham manager this afternoon before his appointment was announced.