After working as a gold miner and a labour organizer in Australia, Savage immigrated to New Zealand in 1907, where he soon became active in the Auckland trade union movement. He joined the Labour Party on its formation in 1916, becoming its deputy leader in 1923 and parliamentary leader in 1933. He greatly contributed to the Labour victory in 1935, when he became prime minister and headed the ministries of external affairs, native affairs, and broadcasting.

As prime minister, Savage gained passage and popular approval of the antidepression economic measures of his finance minister, Walter Nash, and of the educational reform and social-security legislation of his education and health minister, Peter Fraser. After leading Labour to one of its greatest electoral victories (1938) and supporting early mobilization for war (1939), Savage's health declined rapidly. Fraser became acting prime minister until Savage's death, when he succeeded Savage as head of the government (1940–49).