The signing also strikes a blow for the profile of Serie A against La Liga, which has now lost two of its three most famous players in the previous year after Paris Saint-Germain signed Neymar from Barcelona last August.
"Cristiano Ronaldo will always be a symbol of Real Madrid and a reference point for future generations".
The German worldwide joined Liverpool in 2014 and played his 167th and last match for the Premier League side in their Champions League final defeat by Real Madrid in May.
He has scored a record 120 Champions League goals, 105 of them since moving to Madrid - 12 more than Juventus managed in that same period.
Ronaldo, however, soured the celebrations immediately after the 3-1 win over Liverpool in the final in Kiev by indicating he had made a decision to leave, saying in a post-match interview "It was attractive to play for Real Madrid".
Ronaldo, 33, joined Real from Manchester United in 2009 for a then-world record fee of £80million.
The forward has also cemented his place as Madrid's all-time leading scorer with 451 goals in 438 games.
Ronaldo thanked his teammates, the president, the board and all the club staff before departing, saying in the statement: "However, I think the time has come to open a new stage in my life and that is why I have asked the club to agree to transfer me".
During his nine-year spell at the Santiago Bernabeu, Ronaldo won 15 trophies, including two La Liga titles and two Copa del Rey crowns.
Los Blancos are reported as having accepted an offer for their star ahead of what could be one of football's greatest coups - even at the player's age - and he is expected to arrive in Turin very soon.
Marca added that English striker Harry Kane has been linked to Real Madrid as well. "I came here to win titles". According to the Atlanta Journal-Constitution, Ronaldo's Juventus debut could come in the MLS All-Star Game on August 1 at Mercedes-Benz Stadium.
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