Carnett, nicknamed "Lefty", entered the major leagues in 1941 with the Boston Braves, playing in two games before joining the United States Navy during World War II (1942–43). After he was discharged, he played for the Chicago White Sox in 1944 and the Cleveland Indians in 1945, mostly as an outfielder and first baseman. In his three-season career, Carnett pitched 5 innings in six appearances, and posted a 3.40 earned run average with four strikeouts, three walks, and no decisions. His career batting statistics included a .268 batting average with 25 doubles, 8 triples, 1 home run, and 67 runs batted in.