Born in 1737 as the eldest son of the 9th shogun Tokugawa Ieshige. He was doted on by his grandfather Yoshimune and raised with great expectations. He became the 10th shogun in 1760. Intelligent and talented in scholarship and the arts, he was especially passionate about shogi, even publishing a collection of shogi problems titled 'Gosen Shogi Kokaku.' In politics, following his father's wishes, he promoted Tanuma Okitsugu from chamberlain to senior councilor. Tanuma attempted mercantilist policies to restore shogunate finances but fostered an era of bribery and corruption known as the 'Tanuma Era.' Ieharu left governance entirely to Tanuma while devoting himself to shogi and painting. He died in 1786 at age 50.

Intelligent and multi-talented, but more inclined toward hobbies than politics. He inherited his grandfather Yoshimune's ideals of literary and martial arts but depended on Tanuma for actual governance.

His shogi skill was said to rival professional players, making him a uniquely cultured shogun. However, his complete delegation to Tanuma led to governmental corruption, necessitating the later Kansei Reforms. He is considered a shogun of mixed legacy.