Also in 1913, Hann began working as a full-time union organiser. He moved to London, and was active in opposing World War I. In 1934, he chaired a major labour pageant, organised by the Central Women's Organisation Committee of the London Trades Council.[2]
In 1935, Hann was appointed as National Organiser for NAUSAWC then, the following year, he was elected as the union's general secretary. In the role, he was known for his negotiating skills and knowledge of economics.[1] He began working closely with Joseph Hallsworth of the rival National Union of Distributive and Allied Workers, and in 1947 the two unions merged, forming the Union of Shop, Distributive and Allied Workers. Hann was expected to become joint Assistant General Secretary of the new union, but resigned to work full-time for the Industrial Court.[1][3]