radical labour leader, founder and member of numerous British labour unions and organizations.

Mann joined the Amalgamated Society of Engineers in 1881 and in 1885 affiliated himself with the socialist movement. He first gained national prominence as coleader, with John Burns, of the great London dock strike in 1889. In the 1890s he served as secretary to James Keir Hardie's newly formed Independent Labour Party. During the first decade of the 20th century, Mann was active in Australia as a union organizer; after he returned to England, he helped the trade unionist Ben Tillett found the National Transport Workers' Federation in 1910. In the 1920s Mann was an important member of the British Communist Party.