The £25 million deal ends a year-long pursuit of the player by United boss Sir Alex Ferguson.
Berbatov was always Ferguson's No1 one target. He has had three bids rejected - last summer, in the New Year and at the end of this season.
Ferguson said last week: "We are looking at three or four different options about the strike department which we hope will come to a happy conclusion.
"Hopefully, we will have someone in for the start of the season."