Organized as the Workingmen's Party in 1876, the Party was renamed in 1877. In 1890, the SLP came under the leadership of Daniel De Leon. Since then, the SLP has adhered to the form of orthodox Marxism known as DeLeonism.
De Leon's opponents, led by Morris Hillquit, left the SLP in 1901 and fused with Eugene Debs's Social Democratic Party and formed the Socialist Party of America. The SLP also lost membership of militant Marxists to the Communist Party of America and the Socialist Workers Party of America.
In 1976, the SLP nominated its last Presidential candidate, and has ran few campaigns since then.