One of the worst-kept secrets within football finally became public knowledge when the Netherlands manager was named as the new boss of the struggling English giants.
United's record appearance holder Ryan Giggs will be his assistant after announcing he was ending his playing career.
Van Gaal, 62, has signed a three-year contract to succeed David Moyes who was sacked in April after a disastrous run of results culminating in failure to qualify for the Champions League.
A disciplinarian who has rarely lacked confidence in his own ability, van Gaal has won domestic titles and cups with Ajax, AZ Alkmaar, Barcelona and Bayern Munich as well as guiding Ajax to Champions League glory.
And he was in no doubt he could enjoy more success in what will be his first job in English football.
"It was always a wish for me to work in the Premier League," van Gaal explained.
"To work as a manager for Manchester United, the biggest club in the world, makes me very proud.
"I have managed in games at Old Trafford before and know what an incredible arena Old Trafford is and how passionate and knowledgeable the fans are.
- 'Big ambitions' -
"This club has big ambitions. I too have big ambitions. Together I'm sure we will make history."
However, his duties with the Dutch national side mean van Gaal will not be able to join up with United until after the World Cup in Brazil, which would not be until mid-July if the Netherlands reach the latter stages of the tournament.
Giggs, 40, who was in charge for the final four games of the season after Moyes's departure, said: "I am thrilled to have the chance to serve as assistant manager.
"Louis van Gaal is a world-class coach and I know I will learn a lot about coaching from being able to observe and contribute at such close quarters," Giggs added.
United executive vice-chairman Ed Woodward said the club had "secured the services of one of the outstanding managers in the game today".
And United striker Wayne Rooney welcomed his new boss by tweeting: "Great to see Louis Van Gaal has been named @ManUtd manager. Looking forward to working with him."
Chelsea manager Jose Mourinho, who worked under van Gaal at Barcelona and later denied him a second Champions League title when his Inter Milan side beat the Dutchman's Bayern Munich in 2010, also had warm words for the new Old Trafford supremo.
"He is a great football manager and I am happy he joins me in the same country and the Premier League," Mourinho said.
"But more important than that, he's a great guy, a great man and I wish him good," the Portuguese added.
Van Gaal quickly emerged as the favourite to take over at Old Trafford after Moyes was dismissed.
Moyes was the handpicked successor of former United manager Alex Ferguson after his compatriot retired as British football's most successful boss at the end of last season.
But the former Everton manager struggled to adjust to life at Old Trafford and was sacked less than 12 months into a six-year contract after United failed to qualify for next season's Champions League -- something Woodward reckoned had cost the club in the "mid-pound sterling30 millions".
United finished the season in seventh place and had to watch neighbours Manchester City win the title.
Van Gaal is set to rejuvenate an aging squad with major changes in defence expected after the long-established centre-back pairing of Nemanja Vidic and Rio Ferdinand both announced they were leaving the club.
United's US-based owners, the Glazer family, also want van Gaal to restore the reputation of the club's youth system as a conveyor belt for first-team talent, something Moyes was said o have little interest in during his brief time at Old Trafford.
"I am delighted that Louis will be our next manager," said Joel Glazer.
"He has an outstanding pedigree as a coach, both as a man who motivates his teams to win trophies and as someone who believes in giving young players a chance to prove their worth."