Ohtani expressed a desire to move directly to the major leagues after high school and received interest from numerous teams including the Texas Rangers, Boston Red Sox, New York Yankees and Los Angeles Dodgers. On October 21, 2012, he announced that he would pursue a career in Major League Baseball (MLB) rather than turn professional in Japan.
Ohtani made his debut at age 18 in the Fighters' season-opening game on March 29, 2013, playing as a right fielder. He was selected for a Pacific League roster spot for the 2013 All-star game. As a pitcher, he finished the season with a 3–0 record in 11 starts. In 2017, he played in 65 games, hitting .332 with eight homers and 31 RBIs while posting a 3–2 record, a 3.20 ERA, and 29 strikeouts as a pitcher. In September, it was revealed that Ohtani would ask to be posted at the end of the season to play in Major League Baseball in 2018. However, before that could happen, he had surgery on his right ankle in early October. The injury had originally occurred in the 2016 Japan Series and had cost him a chance to play in the 2017 World Baseball Classic in addition to restricting his playing time during the season. On November 21, 2017, MLB and NPB came to a posting agreement for Ohtani. Ohtani narrowed his finalists to seven teams, signing with the Angels for a $2.315 million bonus.
On December 9, 2017, Ohtani signed his deal with the Los Angeles Angels. Ohtani's debut MLB spring training in 2018 was disastrous and the majority of American news sources were extremely disappointed, concluding that he could not accomplish even one of his two-way abilities. By the end of Ohtani's impressive 2018 MLB regular season, the American media admitted they wrote off Ohtani far too early. On August 18 2021, Ohtani hit his 40th of the year, becoming the first left-handed batter in Angels history to reach 40 home runs, surpassing lefty Reggie Jackson's 1982 record of 39. Ohtani was unanimously voted the American League Most Valuable Player, becoming the 23rd pitcher and first designated hitter to win the award.
Later in 2023, Ohtani was yet again unanimously voted the American League Most Valuable Player, becoming the first player in MLB history to win MVP by unanimous vote twice. He was also named to the 2023 All-MLB Team, becoming the first player to ever be named to both first teams in the same season (as a designated hitter and starting pitcher respectively). He won his third straight Edgar Martínez Outstanding Designated Hitter Award, his second Silver Slugger Award for being the best offensive player at the designated hitter position in the American League, and his first career AL Hank Aaron Award. For the third straight year, the Angels announced that Ohtani was once again the team's Los Angeles Angels Player of the Year of 2023, as voted by his teammates. Ohtani's contract expired after the 2023 season and he became a free agent for the first time in his career.
On December 11, 2023, Ohtani signed a 10-year, $700 million contract with the Los Angeles Dodgers, the largest contract in professional sports history at the time. Because of an elbow injury and consequent surgery in September 2023, Ohtani and the Dodgers announced that he would not pitch in the 2024 season. Ohtani debuted with the Dodgers as the designated hitter on March 20. On April 21, Ohtani hit the 176th home run of his career, passing Hideki Matsui for the most by a Japanese player in MLB history. On August 3, Ohtani joined the 30–30 club—30 home runs and 30 steals in a season—in his 108th game, becoming the third-fastest player in Major League history to do so. He became the first and only player in MLB history to hit 50 home runs and steal 50 bases in a single season. He also became the 16th player in MLB history to reach 10 or more RBI in a single game, and the first since July 7, 2018. After the 2024 season, with his 50–50 performance, Ohtani won the National League Most Valuable Player award unanimously.
By the end of his second season, Ohtani won his fourth career MVP award unanimously—his second consecutive NL MVP and third consecutive overall, became the first player in Major League history to win multiple MVPs in both leagues and only the second player to win four MVP Awards after Barry Bonds, was one of two players to win MVP in at least three consecutive seasonsm received his fifth straight Edgar Martínez Outstanding Designated Hitter Award, and received the Hank Aaron Award for the third straight year.
