The Italian champions announced the huge transfer coup on their official website at 6pm BST, shortly after Ronaldo had penned an open letter to Madrid supporters.
A short statement from Juve clarified the length of the Portugal international's contract, which reports suggest is worth £500,000 a week, and welcomed him on board.
"He's called Cristiano Ronaldo and he's now officially a Bianconero!" the statement read. "Juventus are delighted to announce that the five-time Ballon d'Or winner has signed for the club on a four-year contract until June 30, 2022."
A separate press release revealed that Juve have two years to pay the transfer fee to Madrid, worth just over £100m when accounting for all additional costs.