Van Gaal has signed a three-year contract, while caretaker manager Ryan Giggs will stay on at United, taking the role of assistant manager under the new regime. Frans Hoek and Marcel Bout have also joined as assistant coaches.
"It was always a wish for me to work in the Premier League. To work as a manager for Manchester United, the biggest club in the world, makes me very proud," said the former Ajax, Barcelona and Bayern Munich boss.
"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. This club has big ambitions; I too have big ambitions. Together I'm sure we will make history."
The current Netherlands boss had been widely touted as the successor to David Moyes, who was sacked in April following a miserable Premier League campaign in which United missed out on European football for the first time in 20 years.
United legend Giggs took over the reins at Old Trafford on an interim capacity, acting as a player/manager, and employed the services of Paul Scholes, Nicky Butt and Phil Neville who oversaw coaching duties throughout the remainder of the season.
"United has been a huge part of my life and I'm delighted to be able to continue that relationship in such a key role," said Giggs, who confirmed he was ending his 23 years as a United player.
United executive vice-chairman Ed Woodward added: "In Louis van Gaal, we have secured the services of one of the outstanding managers in the game today.
"He has achieved many things in his career to date and Old Trafford provides him with a fitting stage on which to write new chapters in the Manchester United story."
Executive co-chairman, Joel Glazer, said: "I am delighted that Louis will be our next manager. 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. I am sure he will make a big impression on the club, the players and the fans."
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- Ryan Giggs
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