In 1919, he again ran for election as Secretary of the Amalgamated Society of Engineers, this time successfully. He held the post until 1921, when he retired at the age of sixty-five. He welcomed the Russian October Revolution in 1917 and the Communist government, and called for soviets to be formed in the United Kingdom. In 1920, he was one of many members of the British Socialist Party, inspired by the Revolution, who formed the Communist Party of Great Britain. Mann was chairman of the British Bureau of the Red International of Labor Unions and its successor, the National Minority Movement, from their formation in 1921 until 1929.