Blind, 24, had long been expected to join his former Holland boss Louis van Gaal at Old Trafford and the deal was finally signed off just over three hours before the end of the window.
Blind's arrival from boyhood club Ajax takes the Red Devils' spending to around £150million on permanent signings, following the big money acquisitions of Luke Shaw, Ander Herrera, Marcos Rojo and Angel di Maria, the latter becoming Britain's most expensive player having cost £59.7million from Real Madrid.
Blind has agreed a four-year deal with United and his versatility will provide options for Van Gaal, whose initial attempts to shift United to 3-5-2 have proved a struggle.
Blind is comfortable across the back line, at wing-back or as a defensive midfielder.
He told United's official website: "It is a real honour to sign for Manchester United.
"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."
The United boss added: "I am delighted Daley has signed for the club.
"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."
Source : PA
Source: PA