The Red Devils signed the veteran goalkeeper as a back-up in 2018 and he made only two appearances for the club, in the Carabao Cup and Europa League, before hanging up his gloves on Thursday.
“After 511 appearances, I’ve decided it’s the right time to move into the next stage of my career,” he told the club website. “There have been so many fun moments mixed in with the odd challenge, but I’m grateful for each and every one.
“Fulfilling a boyhood dream of playing for Manchester United was something I thought was out of reach, so to have achieved that fills me with great pride and emotion!
“Although I haven’t played as many games in the last four years, I’ve given everything to the group every single day on the training pitch and in the dressing room. The opportunity to join the biggest club in the world was one I could never turn down and I’m so grateful for the lessons learned and the friends I’ve gained.
“The opportunity to challenge, set standards and ultimately learn from some truly exceptional players and staff has been so valuable.”
Grant spent most of his career in the second-tier after breaking out with Derby in the 2002-03 season.
He added: “I’ve been extremely fortunate to play for some amazing clubs, Derby County, Oldham Athletic, Sheffield Wednesday, Burnley, Stoke City and now to finish at the pinnacle – Manchester United.
“I’m thankful to each and every club for what they have given to me, each one has shaped me into who I am. The relationship with the supporters of these great clubs will always be one of my most treasured memories.”