O-Ie Sōdō
Tsunamasa was born in Edo in 1661 as the eldest son of Matsudaira Masakatsu of Echizen-Matsuoka Domain and his mother was a daughter of Tokugawa Ieyasu's uncle, Matsudaira Sadayuki. HIs name in infancy was Senkiku (仙菊), later becoming Matsudaira Tsunanobu (綱宣). In 1674, when his uncle Matsudaira Masachika became "daimyō" of Fukui Domain, an "O-Ie Sōdō" erupted between followers of Masakatsu and Matsudaira Mitsumichi's illegitimate son, Naokata. Although the dispute was settled in favour of Masachika, the faction favouring Masakatsu remain vehemently opposed to his rule, and blocked any action he attempted to take. Masachika decided to retire after two years, and appointed Masakatsu's son Tsubanobu as his successor. Tsunanobu changed his name to Tsunamasa at this time. He was granted Senior Fifth Rank, Lower Grade Court rank and the courtesy title of "Echizen-no-kami" the same year. His courtesy title was raised to "Sakon'e-gon-shōjō" in 1680.