His father was Tayasu Munetake and he was the grandson of the eighth shogun Tokugawa Yoshimune. The Tayasu house held different beliefs than the others living in Edo Castle. They lived a lifestyle that was more strict. The Tayasu following the example set by Yoshimune. In Munetake's words, the praise of manly spirit ("masuraoburi") as opposed to feminine spirit ("taoyameburi"). This set them apart from the rest of the family. Munetake thought he would rule after his father died. This did not happen. Yoshimune's eldest son, Ieshige became ruler. Because of this, Sadanobu was raised under the belief that he would be the next heir to the title of Shogun. His education growing up was very good. He was taught along Confucian lines. By the time Sadanobu was in his teens, he had already learned much of the teachings of Confucius. As he grew older, many expected more strongly for Sadanobu do well because many members of the Tayasu house began to die young. The family tried many ways to make Sadanobu as the next shogun. Their attempts were stopped by the political clique of Tanuma Okitsugu. Okitsugu was the chief rōjū at that time.