Ed Woodward will step down from his role as executive vice-chairman before leaving the club in April.
Arnold, who will succeed Woodward in running the club, has been the driving force behind numerous commercial deals.
Woodward will attend football board meetings until the end of the season, but he won't be involved in the day to day running of the club.
Arnold said he was honoured to serve the club and its fans. I want to return that honor in any way I can.
"I would like to thank Ed for his dedication to Manchester United during his nine years as executive vice-chairman and 16 years as a member of the club," said the executive co-chairman. We are looking forward to Richard and his leadership team opening a new phase in the club's evolution, with ambitious plans for investment in Old United, the strengthening of our engagement with fans, and continued drive towards our most important objective - winning on the pitch."
Woodward's time at the club is drawing to a close, even though United announced in April of 2020 that he would be leaving at the end of last year.
Woodward was appointed to the club's board of directors in 2012 and took charge of operations after the retirement of David Gill.
Woodward did not have a title under his watch.
The world record fee to bring Paul Pogba back to Old United was one of the transfer fees spent by Manchester United. The club have failed to win a title during Woodward's tenure, despite the fact that notable players such as Marcus Rashford and Mason Greenwood have graduated from the academy. Sir Alex Ferguson was the manager who had won five of the previous seven.
Since Woodward took over, United have only won one trophy, the FA Cup, and one League Cup, with the permanent managers failing to come close to replicating their glory days.
The permanent boss is expected to be named in the summer.
The Woodward era saw significant commercial deals that boosted off the pitch revenues and operating profit.
In the wake of the collapse of the European Super League proposals, which the club had initially been a part of, Woodward said that he was proud to have served United and that it had been an honor to work for the world. It will be difficult to leave the club because it is well-positioned for the future.
During the time I was at Old United, we won the FA Cup, the EFL Cup and the Europa League. I'm proud of the club's culture and return to the Manchester United way of playing.
I am certain that with the changes we have made on-field and to the coaching and football staff in recent years, this great club will soon be lifting silverware again. It deserves it.
Who is Richard Arnold?
Arnold will become one of the most powerful figures in British sport after being promoted to the chief executive's job.
Arnold, who is from the north west, has worked for United for over 14 years, first as the club's commercial director and then as the group managing director.
As group managing director he has had an active track record of fan engagement, including his role as chair of the Fans' Forum and dialogue with supporters' groups. He has supported expansion of junior discounts, barrier seating, and a trial of safe standing, as well as no increase in season ticket prices for the past 10 years.
He will be the first person to hold the title of CEO since David Gill left.
The Woodward era was a success despite the regrets on the pitch.
Sky Sports News' Kaveh Solhekol.
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Sky Sports News' Kaveh Solhekol looked at the impact of Ed Woodward on Manchester United.
It hasn't been good enough on the pitch, if you look at his record. He would be the first person to say that the club has made mistakes, they haven't won the title since Sir Alex Ferguson left, and there's been a lot of turnover in managers. We went from stability to having lots of different managers.
Woodward has done a great job off the pitch. Since he's been at the club, the revenues have doubled and the operating profit has doubled. The training ground and stadium need to be redeveloped, but that is going to be done.
It's been a mixed picture under Woodward.
A lot of the criticism is fair. He wouldn't have been criticized as much if he'd left them to run the football side of things, and then Woodward could have concentrated on things off the pitch.
They didn't get the manager appointment right. They gave David Moyes too much responsibility and there wasn't a structure at the club. They needed a director of football, a technical director and a manager. They now realize that was a mistake.
The style of football was not right when they had Louis van Gaal, he was a fantastic character, box office, and you can't argue with his record, but the style of football was just not right. A lot of Manchester United fans were bored by the football produced by Van Gaal. He had a great relationship with Woodward.
We know what happened after they had Jose Mourinho, although he's on good terms with Woodward as well. The job Woodward did was great and the trophies were brought to the club. It didn't work out for Ole Gunnar Solskjaer, who looked like he was going to achieve something.
The record of United while Woodward was there is not as bad as people think. It's not as bad as what happened under David Gill and Sir Alex Ferguson, but they finished above them in three of the last six seasons and above them in four of the last six seasons. We need some perspective. Woodward said 'I did make mistakes'.
I think the European Super League played a big part in his decision to step down. I don't think Woodward thought that the European Super League would actually happen. The executives used it as a negotiating tool to get what they wanted. He was surprised it happened. When it became apparent that it was going to be a closed league, he came out and said that he was going to resign.
The players at Man Utd are not sure about Rangnick's suitability.
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There are highlights from Manchester United's defeat to Wolves.
Some of the Manchester United players are unsure of the right man to be in charge of the club.
A source has told Sky Sports News that some of the United players are finding it hard to play in the 4-2-2-2 formation.
Sky Sports News has been told that the players at Manchester United are ready to play, but they don't have the coach to get the best out of them.
Paper Talk is live at the Transfer Centre.
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The same source said that the club had to close their training ground in December because of a Covid outbreak and that this had an effect on performances.
Wolves beat United at Old Trafford on Monday night, their first win at the place in over thirty years.
In his first game against Crystal Palace, United struggled to adapt to the high-pressing style of play, but have gone on to win againstNorwich andNewcastle.
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