He studied law at the Tokyo Imperial University.
After studying, Hatoyama was elected assemblyman in the Tokyo city administration.
In 1915 he was elected to the lower house of the Diet and in subsequent years he was reelected 12 times. Opposing the militaristic clique that became powerful before World War II, Hatoyama was politically inactive from 1937 to 1946. In the latter year he formed the Liberal Party, the largest in Japan, which, despite its name, was conservative in outlook. In the elections of that year the party won a plurality and Hatoyama was designated to Emperor Hirohito as the next premier; however, Gen. Douglas MacArthur barred him from taking his seat in the Diet. The occupation authority's order charged that during the Tanaka cabinet (1927 - 1929), of which Hatoyama was chief secretary, he had helped to suppress free speech and to regiment labor and had supported Japanese conquest of China; it also cited Hatoyama's book "Face of the World" (1938), in which he made favorable statements about Adolf Hitler and Benito Mussolini.
Although Hatoyama denied the charges, maintaining that he had no authority in the Tanaka cabinet and that the statements in his book were mere political expediency, he was forced to retire from politics until he was "depurged" in 1951. After two years of illness following a stroke, Hatoyama joined with the Progressive Party to form the Democratic Party and was appointed premier in 1954. His principal accomplishment during two shaky years in power was negotiation of a peace treaty with the Soviet Union, enabling Japan to take a place in the United Nations, from which it had been barred by Soviet veto in the Security Council. Hatoyama resigned in December 1956.