In 1941 he enrolled at Keio University, as a Literature major, where Haga also joined the camera club, often to the neglect of his studies.
Lectures by the folklorist Shinobu Orikuchi (1887–1953), which he joined when he heard that credits were offered to anybody for attendance, were a strong influence on his future interests.
During the war he was recruited to make aerial photographs for the navy, and in 1946 found employment with the Nippon Telegraph and Telephone company.
[4] In 1950 Haga was one of the founders of the Japan Professional Photographers Society (JPS) of which he became chairman for seven years in 1981.
In 1955 a photograph of a heavily pregnant woman against a blurred street scene by Hideo Haga (Pregnant Japanese Woman Hurrying on Her Way, 1952) was selected, for its (then) unusual public perspective on pregnancy,[5] by Edward Steichen for MoMA’s The Family of Man exhibition which was seen by nine million people as it toured thirty-seven countries.