William Mailly (November 22, 1871 – September 4, 1912) was an American socialist political functionary, journalist, and trade union activist.
[2] Mailly became involved in the trade union movement as a member of the United Mine Workers of America in 1893.
Following his blacklisting from the mines, Mailly began to work as an organizer on behalf of the UMWA and the Socialist Party of America.
In 1896, he joined the Socialist Labor Party of America (SLP), but his stay in that organization proved to be short-lived, as he left the SLP in July of the subsequent year to join the Social Democracy of America, an organization which included Victor L. Berger and Eugene V. Debs.
[2] From there Mailly moved to the socialist enclave of Haverhill, Massachusetts, where he served as secretary of the SDP's state and municipal campaign committees.
[5] The January 1903 meeting of the governing National Committee of the SPA elected Mailly as the new Nati Secretary of the party and he assumed these duties the following month.