A switch-hitter who threw right-handed, he played semipro ball in the St. Louis area after high school, and briefly appeared as a catcher for the Indianapolis ABCs in 1938.

After the tryout was observed by coaches Hugh Duffy and Larry Woodall, he was turned away along with Marvin Williams and Jackie Robinson, as the Red Sox had no plans to integrate their roster.

[2] Jethroe returned to the Buckeyes and won his second consecutive batting title with a .393 average, again leading the league with 10 triples and 21 stolen bases.

[2] The Buckeyes won the pennant under player-manager Quincy Trouppe with a 53–16 record, and swept the Homestead Grays – loaded with aging stars such as Cool Papa Bell, Buck Leonard and Jud Wilson – in the Negro World Series.

Before the 1954 season he was one of six players acquired by the Pittsburgh Pirates in exchange for infielder Danny O'Connell, but Jethroe played only two games for the team, the last on April 15.

Despite being among the league leaders in hits, runs and stolen bases during that period, his batting averages generally declined, and he never got another chance in the majors.

[2] After his baseball career ended, Jethroe settled in Erie, Pennsylvania, where he worked in a local factory for several years, played in the city's semi-pro Glenwood League, then opened a bar.

In 1994, Jethroe sued Major League Baseball in order to collect pension payments, as he was one of a host of other former Negro leaguers who couldn't qualify because of the racial discrimination of the 1940s and 1950s which delayed their professional careers.