Despite months of negotiation to sign a new Real Madrid contract, on 10 July 2018, Ronaldo signed a four-year contract with Italian club Juventus after completing a €100 million transfer, which included an additional €12 million in other fees, and solidarity contributions to Ronaldo’s youth clubs. The transfer was the highest ever for a player by an Italian club.
On 16 September, Ronaldo scored his first goals for Juventus in his fourth appearance for the club in a 2–1 home win over Sassuolo in Serie A. His second was the 400th league goal of his career. On 19 September, in his first Champions League match for Juventus, he was sent off in the 29th minute for “violent conduct”, his first red card in 154 Champions League appearances. Ronaldo became the first player in history to win 100 Champions League matches, setting up Mario Mandžukić‘s winner in a 1–0 home victory over Valencia, which sealed Juventus’s passage to the knock-out stages of the competition. In December, he scored his tenth Serie A goal of the season, from the penalty spot, netting the final goal in a 3–0 away win over rivals Fiorentina; with this goal, Ronaldo became the first Juventus player since John Charles in 1957 to score 10 goals in his first 14 league games for the club. After placing second in both the UEFA Men’s Player of the Year and The Best FIFA Men’s Player for the first time in three years, behind Luka Modrić, Ronaldo performances in 2018 also saw him voted runner-up for the 2018 Ballon d’Or, finishing once again behind his former Real Madrid teammate.
Ronaldo won his first trophy with the club in January 2019, the 2018 Supercoppa Italiana, after he scored the game-winning and only goal from a header against A.C. Milan. On 10 February, Ronaldo scored in a 3–0 away win over Sassuolo; the ninth consecutive away game in which he had scored for Juventus in the league, which enabled him to equal Giuseppe Signori‘s single season Serie A record of most consecutive away games with at least one goal. On 12 March, Ronaldo scored a hat-trick in a 3–0 home win against Atlético Madrid in the second leg of the Champions League round of 16, helping Juventus overcome a two-goal deficit to reach the quarter-finals. The following month, Ronaldo scored his 125th goal in the competition, opening the scoring in a 1–1 away draw in the first leg of Juventus’ quarter-final against Ajax, on 10 April. In the second leg in Turin on 16 April, he scored the opening goal of the match in the first half, but Juventus eventually lost the match 2–1, and were eliminated from the competition. On 20 April, Ronaldo played in the Scudetto clinching game against rivals Fiorentina as Juventus won their eighth successive Serie A title after a 2–1 home win, thereby becoming the first player to win league titles in England, Spain and Italy. On 27 April, he scored his 600th club goal, the equaliser in a 1–1 away draw against rivals Inter. Finishing his first Serie A campaign with 21 goals and 8 assists, Ronaldo won the inaugural Serie A Award for Most Valuable Player.