[1] Ōya was born in what is now part of the town of Meiwa in Gunma Prefecture, where his father was a high school principal and his grandfather had been a samurai in the service of Kawagoe Domain.

On graduation he joined the zaibatsu Suzuki Shoten, and from 1925 went to work for Teijin, eventually becoming its president in November 1945.

In his early career, he was praised as a charismatic manager, who introduced new synthetic fibers which made Teijin a market leader in the fabric industry.

However, he later was criticized for over-diversification, and for his refusal to surrender authority over the company despite his obvious mental decline in old age, which led Teijin to the brink of bankruptcy.

In 1947, Ōya was elected to a seat in the Diet of Japan in 1947 Upper House election from the Osaka electoral district, and was reelected for a second term, serving until June 1956 under Liberal Democratic Party (LDP) banner.