Sir Jim Ratcliffe has said it will take "time and patience" to "bring sporting success" back to Manchester United.
The British billionaire has agreed to buy a 25% stake in the Old Trafford club for about $1.3bn (£1.03bn).
His Ineos Group will take control of football operations and Ratcliffe will also provide $300m (£236m) for future investment into United's stadium.
Ratcliffe has told supporters "we recognise our responsibility as custodians of the club on your behalf".
In an open letter to fans, he added: "I believe we can bring sporting success on the pitch to complement the undoubted commercial success that the club has enjoyed.
"It will require time and patience alongside rigour and the highest level of professional management.
"You are ambitious for Manchester United and so are we. There are no guarantees in sport, and change can inevitably take time but we are in it for the long term and together we want to help take Manchester United back to where the club belongs, at the very top of English, European and world football.
"I take that responsibility very seriously."
United say the deal for Ratcliffe to buy his stake in the club is "subject to customary regulatory approvals" but they are "hopeful it will be completed as soon as possible".
There is initially going to be a six-to-eight week process for the deal to be ratified, which includes being signed off by the Premier League.
Ratcliffe added: "Please note that, as with any deal, it is subject to the usual regulatory sign-off process and therefore we do not expect to speak publicly about club matters until after the deal has completed."
United will host Aston Villa on Tuesday at 20:00 GMT and, while Ratcliffe will not be at the game, Ineos director of sport Sir Dave Brailsford will be in attendance.
The former British Cycling chief is set to sit on a powerful three-person committee running the football operations at the club.
"During the process I was kept informed all the time and I think it's very positive they stepped in," said United manager Erik ten Hag before the Villa game.
"We are looking forward to working with them. They want to work with us and we want to work with them. It's very beneficial to Manchester United."
