The Serie A champion swooped to sign the Portugal captain after he indicated that he was considering leaving Madrid after the Champions League final win in May, goal.com reported.
On Tuesday, Juventus president Andrea Agnelli flew from Pisa to Greece to meet Ronaldo, who is on holiday in Kalamata, and his agent Jorge Mendes arrived from England later on to join them.
Ronaldo is said to have agreed a four-year contract that will see him pocket €30 million (£26.5m/$35m) per season and Madrid has since confirmed that it have allowed him to make the move to Turin in a transfer that will cost €100 million (£88m/$117m) plus €12million (£10.5/$14m) in additional charges.
“Real Madrid CF communicates that, in response to the will and request expressed by the player Cristiano Ronaldo, he has agreed to transfer to Juventus FC.”
The announcement was followed by an open letter from Ronaldo, in which he thanked fans for their "love and affection" during his time there.
Ronaldo, 33, reached global superstar status after becoming the world's most expensive player when he joined Madrid from Manchester United in 2009.
During his nine-year spell at the Santiago Bernabeu, Ronaldo won 15 trophies, including two La Liga titles and two Copa del Rey crowns.
He helped Madrid to La Decima in the Champions League final with Atletico Madrid in 2014 and played a crucial role in Los Blancos winning the competition in each of the last three seasons.
And the Santiago Bernabeu club thanked the star for all he had done during his time there, adding to its statement, "Real Madrid wants to express its gratitude to a player who has proved to be the best in the world and who has marked one of the brightest times in the history of our club and world football.
"Beyond the conquered titles, the trophies achieved and the triumphs achieved in the playing fields during these 9 years, Cristiano Ronaldo has been an example of dedication, work, responsibility, talent and improvement... For Real Madrid, Cristiano Ronaldo will always be one of the great symbols and a unique reference for the next generations.
"Real Madrid will always be your home."
Ronaldo, a five-time Ballon d'Or winner, will now have the chance to win a European league title with a third club after completing a shock move to Turin.
Madrid, meanwhile, has already denied making bids for Paris Saint-Germain duo Neymar and Kylian Mbappe as the Spaniards prepare for the 2018-19 season under new coach Julen Lopetegui.
The former Spain coach takes over from Zinedine Zidane after the Frenchman surprisingly decided to resign after Madrid beat Liverpool in Kiev.
Spain’s Marca produced one of the most striking pages, documenting each one of Ronaldo's goals for Madrid with the club badges of who scored against, and labelling him "the legend of 451 goals", the FourFourTwo magazine reported.
AS were similarly effusive in their praise of Ronaldo and went with, "Ciao, Cristiano. It was great while it lasted."
Perhaps the mood was best summed up by Sport, who had the headline "Shock Cristiano".
Mundo Deportivo mocked up an image of Ronaldo in a Juventus shirt, merely writing "CR Seven" with a description of the move.
In Italy, La Gazzetta dello Sport succinctly wrapped up the excitement in the Italian media over Ronaldo's arrival with their "Arrivo!" headline.
And Tuttosport also went for a simple, yet elegantly excitable, header merely writing, "Here!"