Blind, 24, is yet to agree personal terms and undergo a medical, but United are hopeful the versatile player will complete his move to Old Trafford before the transfer window shuts on Monday night.
Reports in Holland suggest the agreed fee is 18 million euros (£14.2 million), with United confirming the agreed deal on the club's official Twitter account and adding that a further announcement would be made soon.
The Ajax youth academy product can play in a variety of positions, including left-back and in central midfield.
If Blind complete his move to Old Trafford, he will become the club's fifth summer signing.
Louis van Gaal and Daley Blind (PA Sport)
"I am enormously proud to be at one of the biggest clubs in the world," the 24-year-old Blind told Fox Sports television as his transfer was sealed before the transfer window ends on Monday.
He can play left back and as a defensive midfielder but said it did not matter in which position United used him.
"I don't mind at all, as long as I get minutes on the field," he said.
After watching his team draw against Sunderland and suffer defeats to Swansea and MK Dons, Van Gaal thinks his squad is in need of an overhaul.
Another target is Roma's Kevin Strootman, but he again is also just coming back from injury.
Van Gaal is expected to sell a number of fringe players before Monday night.
Van Gaal will be looking to finally record his first competitive win as United boss at Burnley on Saturday afternoon.
Daley Blind (AFP)
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