Mizuno was born in Saga Prefecture in 1901[2] and attended Soto Zen Daishi Junior High School (known now as Takagawa Gakuen High School/Junior High School) and then Yamaguchi High School. In 1928, he enrolled in Tokyo Imperial University where he graduated from the Department of Indian Philosophy, Faculty of Letters, before entering the same university's graduate school.
In 1935, he became a lecturer at Komazawa University where he was promoted in 1940, as a professor.[2] Mizuno was renowned for specializing in Pali literature.[1] From 1959 to 1962, he was also a professor at the University of Tokyo. From 1976, he served as vice president of Komazawa University and from 1982 as president of Komazawa University.[2] In 1967, he received the Purple Ribbon Medal.