After informally agreeing to take over last week, the Ajax manager, 52, will succeed interim coach Ralf Rangick in the summer.
Mauricio Pochettino, Zinedine Zidane, and Brendan Rodgers were all shortlisted for the post, but Ten Hag impressed Old Trafford bosses throughout the interview process.
After laying out his long-term ambition for building a great squad while playing attractive and offensive football, seasoned winner Ten Hag edged out the competition.
And he hasn't shied away from the massive task that lies before of him at Manchester United.
Ten Hag, on the other hand, wanted to wait until after his team's loss to PSV Eindhoven in the Dutch Cup final on Sunday before signing the contract. United decided to pay Ajax compensation – thought to be in the region of £2.5 million – in the last few days to sign Ten Hag and his assistant Mitchell van der Gaag.
"It is a great pleasure to be chosen manager of Manchester United, and I am hugely delighted by the job ahead," Ten Hag stated after the news.
"I am totally committed to produce a team capable of delivering the success they deserve, knowing the history of this wonderful club and the enthusiasm of the fans." It will be difficult to leave Ajax after these amazing years, but I can guarantee our fans that I will give everything I have to finish this season successfully before moving to Manchester United."
Before taking the post, Ten Hag was eager to obtain numerous assurances from the hierarchy in order to give himself the greatest possible chance of turning the club around.
RB Leipzig showed some interest, but once he realized he'd get the help he required, there was no doubt in his mind that he wanted the United position.
The announcement comes just two days after the Red Devils were humiliated 4-0 by rivals Liverpool, indicating that the club is keen to find a successful replacement for Sir Alex Ferguson.
Ten Hag's strong Champions League and domestic records with Ajax demonstrated that he was up to the task.
"During his four years at Ajax, Erik has proven himself to be one of Europe's most exciting and successful coaches, recognized for his team's attractive, offensive play and devotion to youngsters," United football director John Murtough stated.
"We were very impressed with Erik's long-term vision for returning Manchester United to the level we want to compete at, as well as his ambition and desire to achieve that, in our conversations leading up to this appointment."
"We wish Erik the best of luck as he concentrates on bringing Ajax's season to a victorious conclusion, and we hope to welcome him to Manchester United this summer." Since Fergie's final season in 2012-13, United has not won the Premier League title.
Before turning to Rangnick to steady the ship until the end of the season, the club went through David Moyes, Louis van Gaal, Jose Mourinho, and Ole Gunnar Solskjaer.
Manchester United, on the other hand, is in the midst of their greatest trophy drought since they were demoted nearly 50 years ago.
After a lengthy search, the Old Trafford hierarchy has chosen Ten Hag to lead the club forward.
Ajax have fought tooth and nail to keep Ten Hag at the Eredivisie leaders, with the Dutch coach still committed to finishing the season with Ajax. "I'm glad that it's been finalized and that it's been officially announced," he remarked. That clarity is critical.
"But I'm only interested in one thing right now, and that's the remaining five games. I want to leave this place on a high note by winning the league." We will automatically qualify for the Champions League if we do so. Ajax has a place there."
Edwin van der Saar, the CEO of Ajax and a United legend, said: "Although four and a half years is a good amount of time, we would have preferred to keep Erik at Ajax for a longer period of time.
"He'll be joining one of the world's most prestigious clubs in a terrific league."
"We owe Erik a great debt of gratitude for what he's accomplished with Ajax thus far, but we're not done yet." I'll take a closer look at his leaving at the end of the season.
"For the time being, what counts are the season's final games, in which we all want to bring home the league trophy."
Ten Hag took charge at Dutch minnows Go Ahead Eagles in 2012 to begin his managerial career.
The former centre-back spent two seasons at Bayern Munich II before returning to Utrecht for another two seasons.
Ten Hag took over at Ajax in 2017 and has already helped them win TWO Eredivisie titles - in 2018-19 and 2020-21 - with a third on the horizon this season.