The former Leeds United shot stopper will serve as back-up to Senne Lammens, with current second choice goalkeeper Altay Bayindir expected to leave Old Trafford this summer.
United have already confirmed the signing of Andrey Santos from Chelsea in a deal worth around £56M and are due to announce Youri Tielemans later this week in what has been a busy summer so far.
The Red Devils revealed Darlow on Tuesday afternoon as he penned a contract until June 2028, with the option to extend for a further year.
Speaking on the move, the 35-year-old revealed that he cannot wait to get started and to push the club to the next level.
“I am extremely proud to sign for Manchester United. I’m joining an excellent group of goalkeepers and I’m really looking forward to all pushing each other to ensure that we maintain the highest standards, which this club demands.
“This is a really special opportunity; everyone can see what an exciting time it is for the club and I cannot wait to play my part in supporting my team-mates and helping to drive the group forwards.”
He joins the likes of Rio Ferdinand, Gordon McQueen, and Alan Smith in a small selection of players who have made the move from Leeds to United in what is a rare move.
Darlow has played 279 games, 74 of which have been in the Premier League as he adds a plethora of experience to the United squad.