Tadayo Okubo was born in 1536. He was the son of Tadakazu, a retainer of the Tokugawas.
Tadayo Okubo served Hirotada Tokugawa, father of Ieyasu, and distinguished himself in the Ikkoshu (Shinshu) Trouble (1536) in which priests of the Ikkoshu Sect of Buddhism rebelled. Took part in Ieyasu's battles of Mikatagahara and Nagashino. When he participated in the expedition against the Rojos in Odawara (1590), Hideyoshi Toyotomi praised his disposition of troops and made him Guardian in Odawara. The same year, he was made lord of Odawara with 45,000 koku.