The Portugal winger finished ahead of Didier Drogba of Chelsea and United team mates Ryan Giggs and Paul Scholes in the 60th vote organised by the Football Writers' Association (FWA).
"I am absolutely thrilled and delighted to win such an important award, it is a real honour," Ronaldo told the FWA after being informed of his victory in a poll in which an unusually high number of 12 players received votes.
FWA chairman Paul Hetherington said: "(It) completes a remarkable turnaround for the player, who was so heavily criticised during last year's World Cup for his part in the sending-off of club mate Wayne Rooney when England played Portugal in the quarter-finals.
"It shows in England
The 22-year-old becomes the first United player to win the award since Teddy Sheringham in 2001 and the first Portuguese to land the honour.
Ronaldo was also voted Player of the Year and Young Player of the Year by the Professional Footballers' Association last month.
The winger, who joined United from Sporting Lisbon for 12.2 million pounds ($24.31 million) in 2003, has been in inspirational form this season, scoring 22 goals for United.
Although United were knocked out of the Champions League by AC Milan on Wednesday, they can still scoop a Premier League and FA Cup double.
(Additional reporting by Padraic Halpin)