Born to a farming family in rural Akaiwa District, Okayama (now part of Okayama city, Okayama prefecture), Ugaki graduated from the 40th class Imperial Japanese Naval Academy in 1912. He placed 9th out of 144 cadets, and served as midshipman on the cruisers and . He was commissioned as ensign on 1 December 1913 and was assigned to the battlecruiser . He subsequently served on the battlecruiser , cruiser and destroyer . After his promotion to lieutenant on 1 December 1918, he attended naval artillery school, and was assigned as chief gunnery officer to the destroyer .