On July 24, 2015, the Mets promoted Conforto to the major leagues. He made his debut later that day, picking up his first major league RBI on a groundout, but going 0-3 while becoming the 1000th player to appear in a game for the Mets. The next day, he collected his first major league hit -an RBI infield hit- as part of a 4 hit game. He hit his first major-league home run on August 3 off Marlins' starter Tom Koehler. He finished the season with 9 home runs in 56 games played. The Mets won the 2015 National League pennant, making Conforto the third player in history to have played in the Little League World Series, College World Series, and Major League World Series, along with pitcher Ed Vosberg and catcher Jason Varitek. Conforto hit two home runs in Game 4 of the 2015 World Series, becoming the first rookie to homer twice in a world series game since Andruw Jones in the 1996 World Series.