Foster was born in Calvert, Texas, and began his professional baseball career in 1897. He was a talented pitcher, and by the early 1900s, he was one of the best black baseball players in the country. In 1903, he led the Cuban X-Giants to the "Colored Championship of the World."

In 1907, Foster became the player-manager of the Chicago Leland Giants. He quickly established himself as a successful manager, and in 1911, he founded the Chicago American Giants, one of the most successful black baseball teams of the pre-integration era.

In the early 1920s, Foster began working on creating a stable and financially successful black baseball league. In 1920, he founded the NNL, which consisted of eight teams from major cities nationwide. The NNL was a huge success, and it helped to elevate the status of black baseball. Rube saw his team, the Chicago American Giants, win the Negro National League pennant 1920–22, 26.

Foster served as the NNL's president and treasurer until he died in 1930. He was a tireless advocate for black baseball, and he played a key role in the development of the Negro leagues. In 1981, he was elected to the National Baseball Hall of Fame.