Ronaldo had been with the squad since 2009 and finished with 451 goals in 438 games. He led Real Madrid to 16 championships, with five of those in the Champions League.
Ronaldo released a heart-felt letter to his former teammates and fans, thanking them for the nine-year experience.
The new destination for Ronaldo is Juventus, a Serie A club in Italy. He accepted a transfer to the team worth nearly $140 million.
"Beyond the conquered titles, the trophies achieved and the triumphs achieved in the playing fields during these nine years, Cristiano Ronaldo has been an example of dedication, work, responsibility, talent and improvement," Real Madrid said in a statement.
Ronaldo was recently in the World Cup with Portugal. The team was eliminated in the Round of 16 against Uruguay.