The famous Ayrshire golf resort will be renamed Trump Turnberry, and £100 million has been pledged to renovate the hotel that overlooks the golf course.
Mr Trump said the deal was completed this morning. On a visit to Scotland last month the businessman did not reveal the price tag, only saying that he had paid ''a lot'' for the resort which includes a course on the Open Championship circuit.
It brings the number of golf resorts owned by the property magnate to 17.
Mr Trump said: "I am honoured to own and manage this magnificent property, perhaps the most exciting property there is. We will be spending a great deal of time, effort and money to make Trump Turnberry the finest resort of its kind anywhere in the world."
During a flying visit to Turnberry, and then to his course in Balmedie on the Aberdeenshire coast, in May, Mr Trump said he would only "tweak" the Ayrshire site - and not without the blessing of governing body the Royal & Ancient.
He said: ''We'll bring it to a level that it's never been before.
''It's going to be spectacular. It's rated the number one course in the world and we're going to be working with the Royal & Ancient on certain things that are going to be even more spectacular.
The resort is to be owned and managed by the Trump Organization but the hotel will continue to be managed by Starwood Hotels & Resorts.
Mr Trump is to visit the course next month to discuss his plans for the resort.
A statement released today by the Trump Organization to confirm the purchase said Turnberry had "been the home of four of the greatest Open Championships of all time", including the 1977 "Duel in the Sun" where Tom Watson won over Jack Nicklaus.
Starwood said: "Following completion of the sale of Turnberry Resort to Donald J Trump, Starwood Hotels & Resorts can confirm that the hotel will continue to operate under The Luxury Collection brand as part of a long-term franchise agreement.
"Starwood will work closely with Mr Trump to ensure that the unique guest experiences and personalised service, for which the hotel is renowned, will continue to be offered to guests from around the world."
Mr Trump's first Scottish course in Aberdeenshire opened in July 2012 and it remains "his baby".
Plans for a second golf course, club house and hotel on the same site remain on hold amid a bitter dispute over a proposed wind farm adjacent to the resort.
''This is my baby, I'm very proud of it," he said. "I think we might have built the best course in the world. We've been rated so well.
''As soon as they give up this charade of these terrible, destructive windmills, which are destroying Scotland, we will continue onwards.
''As soon as they stop the craziness, which nobody wants, we will get going.''