The 20-year-old central midfielder has never played a senior match for the Red Devils, but did help the reserve side retain their league title in 2016.
Redmond becomes Scunthorpe's fifth signing of the summer, putting pen to paper on a temporary deal which will keep him at the club until January.
"We've been looking for central midfield players and he was highlighted to us. We know a little bit about him from watching Manchester United games last season, and it was important that we got the right type of character and player to compete with the players we have here. He came across on Wednesday and met me and I met him and his dad. We had a good chat before the game against Sunderland. I wanted him to come over to see how we do things and get a feel for the match day here at Glanford Park," manager Graham Alexander told the club's official website.
"It was down to him to make the decision and he's now agreed to join us on loan. He's got loads of energy. He can handle and pass the ball with both feet and he's an exciting, young talent at Manchester United. They think highly of him and we're really pleased to get him on board with us. His enthusiasm for the game is really evident when I've spoken to him.
"He just wants to play football and wants to make that next step from Under-23s football and make a mark. He wants to show people what he's about. He's got a hunger to improve and do well. He will be in the squad for tomorrow's game, so hopefully we can see what he can do on the pitch.
"He's been playing and training with United, so we know he's fit and ready to go into a game. He will meet the players tomorrow when he gets on the team bus. This group is an easy group to get into, but he'll be straight into the deep end and into tomorrow's game."
Redmond, who will wear the number 18 shirt at Glanford Park, could make his competitive debut for the club when they host AFC Wimbledon in their first game of the new League One season next Saturday.