He graduated with honors from Shirogane Jinjo Elementary School, and later wrote in his memoirs that he first became interested in becoming a writer in the sixth grade, where the daughter of Kosugi Tengai was a classmate.

Osaragi attended Tokyo Imperial University’s Department of Political Science, where he developed a strong sense of resistance to authoritarianism.

In 1924 Osaragi Jirō published his first popular historical novel, Hayabusa no Genji which was serialized in the magazine, Pocket.

However, Osaragi also wrote works of contemporary fiction such as Shiroi Ane ("White Sister") and Kiribue ("Misty Flute").

Kikyō ("Homecoming", 1948) described the author's anger at petty attitudes which surfaced after World War II, and was awarded the Japan Art Academy Prize in 1950.

When he died in 1973 at the age of 75, he was still writing Tennō no Seiki ("Century of Emperors"), a historical chronicle based on the spiritual history of the Japanese people.

When housing developers threatened the mountainside behind Kamakura's famous Tsurugaoka Hachiman-gū, he banded together with a number of famous writers and artists (including Hideo Kobayashi, Nagai Tatsuo, Yasunari Kawabata, Riichi Yokomitsu, Itō Shinsui, Kiyokata Kaburagi), residing in Kamakura to oppose the development.