Jean Servais was a Belgian actor trained at the Brussels Conservatory of Dramatic Arts, where he won the Second Prize.
His acting skills came to the attention of Raymond Rouleau, and he was hired at the Théâtre du Marais, where he acted in Le mal de jeunesse, which was successful in Brussels and in Paris. He was also a member of Jean-Louis Barrault's theatre company.
His first film role was as the simple country dweller who was the victim of an error by the justice system in the film Criminel, directed by Jack Forrester. Servais's film career continued in the 1930s with roles in films such as La Chanson De L'Adieu and La Vie Est Magnifique. After a break in acting during World War II, he returned to the screen with roles in films such as La Danse De Mort.
In the 1950s, he displayed a brooding, haunted demeanor in the crime drama Rififi directed by Jules Dassin, in which he played an embittered and physically ailing leader of a gang of jewel thieves. He appeared in another film directed by Dassin, Celui qui doit mourir, in 1957. He also appeared in La fièvre monte à El Pao, a film written and directed by Luis Buñuel.