The 24-year-old completed his £14 million move from Ajax on deadline day and becomes United's sixth signing this summer following the arrivals of Ander Herrera, Luke Shaw, Vanja Milinkovic, Marcos Rojo and Angel Di Maria.
Blind started every game for Netherlands at the World Cup and is buoyed by the opportunity to link up with Van Gaal once again.
"It is a real honour to sign for Manchester United,” Blind told the club’s official website.
"I have been at Ajax since I was seven years old and I will always have very fond memories of the club and of my time there.
"Louis van Gaal is a tremendously talented coach, I have worked with him at Ajax and also for the Netherlands national team and I cannot wait to work with him at the biggest club in the world."
Blind is capable of playing in central defence, at left-back and in central midfield and Van Gaal admits he was attracted by the Dutchman's versatility.
“I am delighted Daley has signed for the club,” said Van Gaal.
"He is a very intelligent and versatile footballer that can play in many positions.
"Daley is a great reader of the game, he has played under my philosophy over a number of years and he will be a great addition to the team."