He worked as an elementary school teacher in his teens, moved to Tokyo, and managed to secure a position at the first class of the reformed Imperial Japanese Army Academy.

However, the failure of Hamaguchi's economic policies after the start of the Great Depression and his push for demilitarization with the London Naval Treaty of 1930 enraged right-wing ultranationists.

In 1931, although Ugaki refused to cooperate with them, he also failed to punish the insurgents responsible for the March Incident, an attempted coup-d'etat by young officers of the Sakurakai who sought to make him Prime Minister.

Recalled to Japan after the fall of the Hirota Kōki administration, Ugaki was named Prime Minister in February 1937, but was unable to form a Cabinet due to strong opposition from his political enemies within the Army.

Ugaki was highly regarded by Saionji Kinmochi and was perceived as having a moderate foreign policy and being opposed to the increasingly fascistic trends within the military.

After the February 26 Incident in 1936, the Japanese military had obtained a restoration of the requirement that the Army and Navy Ministers must be selected only from active duty officers.

Ugaki had been requested by Konoe for assistance to negotiate a peace settlement with the Republic of China following the Marco Polo Bridge incident to avoid an all-out war.

He was the center of a movement which supported a quick end to World War II, and from 1943 was active in efforts to oust Prime Minister Hideki Tojo from office.

After World War II, along with all former members of the Japanese government, Ugaki was purged from public service and arrested by the American Occupation authorities.