On April 17, 1954, he became the first African American to play for the Cincinnati Reds' franchise, known during the mid-1950s as the Redlegs. Pinch-hitting for pitcher Corky Valentine against Lew Burdette, Harmon flied out in the seventh inning of a 5-1 loss to the Milwaukee Braves at County Stadium. In that game he came to bat after another rookie, Nino Escalera, an Afro-Latin American from Puerto Rico who pinch hit immediately before Harmon to become the first black player to appear for the Cincinnati franchise.