He was the younger brother of political theorist Sakuzō Yoshino, a major proponent of Taishō democracy.

He graduated from Tokyo Imperial University in 1913 with a degree in German law, and was accepted into the Ministry of Agriculture and Commerce.

A protégé of Yamamoto Tatsuo, and as one of few members of the ministry with a legal degree, he rose rapidly through the bureaucratic ranks to the post of Secretary to the Minister of Agriculture and Commerce.

The same year, he became vice-president of Manchurian Industrial Development Company, although his relations with the Imperial Japanese Army were not good.

[6] During World War II, Yoshino served as chairman of the Standing Affairs committee of the Imperial Rule Assistance Political Association and was war-time governor of Aichi Prefecture.