Robinson left college to support his mother, but in 1941 played professional football with the Los Angeles Bulldogs of the Pacific Coast League. He entered the army in World War II and was discharged as a lieutenant in 1945. In Oct., 1945, Branch Rickey, then president of the Brooklyn Dodgers, signed Robinson to play for the Montreal Royals, a Brooklyn farm club in the International League. Despite several incidents in spring training in the South and many inconveniences during the season, Robinson—the first African-American ballplayer in that league—excelled as a second baseman and won the league batting crown.

In 1947 precedent was shattered when Robinson was brought up to the Brooklyn club. African Americans had not played in big-league competition in the 20th cent., but resistance dwindled as Robinson excelled. In 1949 he won the National League batting crown, hitting .342, and was named the NL's most valuable player. Robinson played his entire career (1947–56) with Brooklyn, where he set fielding and batting records and gained a reputation for base stealing. Other African Americans began playing in the major leagues soon after his debut. In 1962 Robinson became the first African American to be inducted into the Baseball Hall of Fame.