Robeson plays Zinga, a black dockworker in England with a great baritone singing voice. He is discovered by an opera impresario, and is catapulted into great fame as an international opera star. Yet he feels alienated from his African past, and out of place in England. By chance, he is informed that an ancestral medallion that he wears is proof of his lineage to African kings, and he leaves fame and fortune to take his rightful place of royalty. Reunited with his people, he plans to improve their lives by combining the best of western technology with the best of traditional African ways.

Song of Freedom may best represent the opportunity Robeson was looking for to "give a true picture of many aspects of the life of the colored man in the West. Previously on the screen, he has been characterized or presented only as a comedy character. This film shows him as a real man." Robeson was also given final cut approval on the film, an unprecedented option at the time for an actor of any race.