In Sheffield, Carpenter became increasingly radical. Influenced by a disciple of Engels, Henry Hyndman, he joined the Social Democratic Federation (SDF) in 1883 and attempted to form a branch in the city. The group instead chose to remain independent, and became the Sheffield Socialist Society. While in the city he worked on a number of projects including highlighting the poor living conditions of industrial workers. In 1884, he left the SDF with William Morris to join the Socialist League. From there he stayed with William Harrison Riley while he was visiting Walt Whitman.