In 1933, Hartnett was selected to be a reserve catcher for the National League team in the inaugural Major League Baseball All-Star Game held on July 6, 1933. It was the first of six consecutive All-Star game selections for Hartnett. At the mid-season point of the 1934 season, Hartnett was hitting for a .336 batting average with 13 home runs to earn the starting catcher's role for the National League team in the 1934 All-Star Game. Hartnett was calling the pitches for Carl Hubbell in the 1934 All-Star Game when the Giants pitcher set a record by striking out future Hall of Fame members Babe Ruth, Lou Gehrig, Jimmie Foxx, Al Simmons, and Joe Cronin in succession. Hartnett ended the 1934 season with another strong offensive performance, hitting for a .299 batting average with 22 home runs and 90 runs batted in. He dominated the defensive statistics, leading the league's catchers in assists, putouts, baserunners caught stealing, caught stealing percentage, range factor and in fielding percentage.