In 1916, Bell was elected to the Clyde Workers Committee, within which he promoted the SLP's policy of industrial unionism. In 1917, he led a successful national strike of engineers and foundry workers. Again prominent in 1919, he was elected President of the Associated Ironmoulders, Secretary of the SLP and editor of its newspaper, "The Socialist". He sat on a unity committee, intending to negotiate for a single communist party with leaders of the British Socialist Party, Workers Socialist Federation and other socialist groups, but their proposals were repudiated by the SLP. Resigning as Secretary, he helped found the Communist Unity Group, which became an original constituent of the Communist Party of Great Britain (CPGB).