On January 14, 2019, LeMahieu signed a two-year, $24 million deal with the New York Yankees. The Yankees anticipated using LeMahieu as a utility infielder. He made his Yankees debut on March 30 at Yankees Stadium, picking up a pair of hits and an RBI in four at-bats in a 5–3 loss to the Orioles. After getting off to a fast start, LeMahieu had an electric month of June. He reached base safely in all but two games, and also put together a 14-game hitting streak from June 14 to June 30 (including six consecutive multi-hit games from June 23-30). In the two-game London Series (which marked the halfway mark of the Yankees season) at the end of June, LeMahieu had seven hits in 12 at bats, three doubles and seven RBIs. This performance helped the Yankees sweep the Red Sox in the series. This won LeMahieu his first career Player of the Week award. He then followed it up by winning the June AL Player of the Month Award for the first time (batting .395/.434/.658 with 6 home runs, 29 RBIs, 26 runs scored, and 45 hits) and being elected as the starting second baseman for the All-Star game.
Despite his 6'4", 215 pound frame that led many scouts to suggest that he had potential as a pure power hitter, LeMahieu became a powerful opposite field contact hitter. His tendency to not leg kick, and hit for contact with low launch angle (average of under 10 degrees) was compensated by his high exit velocity (91.7 mph average as of August 8, 2019), meaning he can still hit for extra bases while not getting long fly outs. He has also hit more opposite field home runs than pulling home runs in the 2019 season.