Realmuto was drafted by the Marlins in the third round of the 2010 Major League Baseball Draft; he was the 104th overall pick. The Marlins converted him from shortstop to catcher in their minor league clubs in North Carolina, Jupiter, Jacksonville, and New Orleans. Realmuto was added to the Marlins' 40-man roster on November 20, 2013.
Realmuto was called up to the major leagues for the first time on June 1, 2014. He batted .241 with 9 RBIs in 11 games. On June 5, he recorded his first career hit off of Jake Odorizzi against the Tampa Bay Rays in an 11-6 win.
While Realmuto joined the Marlins for spring training, he was sent to Triple-A to start the season. In the second week of the season, he was called up to fill in for injured catcher Jeff Mathis, and went 2-for-3 in his first season appearance on April 13 in a 2-3 loss to the Atlanta Braves. At the end of April 2015, the Marlins designated catcher Jarrod Saltalamacchia for assignment and promoted Realmuto to the starting catcher position.
