Portugal international Ronaldo, the World Footballer of the Year, becomes the third confirmed signing under new Real president Florentino Perez, who has returned to the club pledging to create a "spectacular sporting project".
Perez spent around $93 million on AC Milan's Brazilian playmaker Kaka and has also brought in Spain defender Raul Albiol from Valencia for a reported fee of $21 million.
Six seasons
"Real Madrid and Manchester United have signed the final agreement for the transfer of the rights of the player Cristiano Ronaldo effective July 1," Real said on their website.
"The player will remain at Real Madrid for the next six seasons and will be presented on July 6 at the Bernabeu stadium," the statement said.
Real and Ronaldo's representatives had been negotiating personal terms since United announced this month they had accepted the Madrid club's offer.
There were no details of the agreement in the Real statement. Spanish media have reported that Ronaldo will earn around $18 million per season.
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