Clemens Palme Dutt was the elder brother of Rajani Palme Dutt. Both were active in the Communist Party of Great Britain. Clemens worked as a journalist, translator and editor, in particular of the works of Marx and Engels. The brothers’ Communist ideals were influenced from an early age by their father Dr Upendra Krishna Dutt’s activities as a doctor in a working-class part of Cambridge. While at university, Clemens and Rajani were involved with the Socialist Club where both came to the attention of the British authorities and remained under constant surveillance. Both brothers were founding members of the Communist Party of Great Britain (CPGB).

In the 1920s, both brothers were writing for Labour Monthly and for a time Clemens took over from his brother as editor. In the 1920s, he became actively involved with the Indian independence movement. Working as a journalist in London, he wrote in particular on India and the Indian independence struggle. In July 1923, he visited Berlin from Moscow, where he became closely associated with M. N. Roy, who was heading the Indian section of Comintern. He returned to London later that year under instructions from Comintern to assist Shapurji Saklatvala. In 1925, the CPGB established its own colonial bureau, which Clemens Palme Dutt headed. The bureau attempted to form connections in India, Palestine, China, Egypt and Ireland. He became the link between the CPGB colonial bureau the Comintern’s Indian section and Indian Communists in Europe and India. In 1927, together with N. J. Upadhyaya and Ajoy Banerji, he founded the Indian Seamen's Union in London. By then he was also on the London Council of the Workers' Welfare League of India, working in close cooperation with Saklatvala. During this period Palme Dutt visited Liverpool several times to help with the organization of Indian seamen by local Communists active in the port.

In March 1928, Clemens Palme Dutt was asked by Reginald Bridgeman to join the Executive Committee of the British Section of the League Against Imperialism. In 1928, Palme Dutt returned to Moscow as a member of a sub-committee of the Executive Committee of the Comintern to advise on the Indian situation. In the 1930s, he worked on the editorial staff of the Daily Worker, the organ of the Communist Party of Great Britain, and acted as the Chairman of the Indian Section of the Communist Party of Great Britain. He also represented the Indian Seamen’s Union on the Executive of the League Against Imperialism. Palme Dutt worked as part of the Meerut Prisoners’ Defence Committee. In August 1930, he replaced Percy Glading as head of the Colonial Department of the CPGB. In 1930, together with Saklatvala, he helped to found the Workers' Section of the London Branch of the Indian National Congress. In June 1931, he was part of a sub-committee of the Colonial Bureau of the CPGB to organize Indian students in Britain.

In late 1931 he moved to Berlin and later to Moscow where he met Violet Lansbury (daughter of George Lansbury, leader of the Labour Party in the early 1930s) whom he married in 1936 and with whom he had a daughter. During the Spanish Civil War, Palme Dutt worked together with Krishna Menon and the India League to collect donations for an ambulance for Spanish Republicans. By early 1939 Palme Dutt, his wife and daughter had returned to Britain permanently. He continued to work for the CPGB, addressing meetings and writing articles.