Although Gernert spent much of the 1950s with the Red Sox, he often found himself sharing the first-base job with players such as Vic Wertz, Norm Zauchin and Mickey Vernon. A powerful right-handed batter, he was signed to take advantage of the Green Monster at Fenway Park. Gernert batted a career-high .291 in 1956 and topped the 20-homer mark in 1953 and 1958.
Gernert was involved in the first interleague trade without waivers in baseball history, on November 21, 1959, when Boston shipped him to the Cubs for first baseman Jim Marshall and pitcherDave Hillman.[2] Gernert helped the Reds win the 1961 National League pennant, as a pinch hitter; however, in that World Series, which the Reds lost to the New York Yankees in five games, he was 0–4 in pinch-hitting roles.