Sixth son of Oda Nobunaga's retainer Mori Yoshinari, and younger brother of Mori Ranmaru, who died alongside Nobunaga at Honno-ji. After serving Toyotomi Hideyoshi and then Tokugawa Ieyasu, he was rewarded for his service at Sekigahara with the 186,000-koku Mimasaka domain in 1603. In 1604 he began building Tsuyama Castle, renaming the site from Tsuruyama ("Crane Hill") to Tsuyama, and completed the 13-year project in 1616 — one of Japan's Three Great Hirayama Castles. He died suddenly in 1634 while accompanying the third shogun Iemitsu to Kyoto, aged 65.

Inheriting the martial reputation of the Mori family, including that of his brother Ranmaru, he also proved himself a capable administrator, patiently completing the 13-year castle project that laid the foundation of Tsuyama.

The founder of both Tsuyama Castle and the city's name. The castle's magnificent stone walls, counted among Japan's Three Great Hirayama Castles, are cherished today as Tsuruyama Park.