Tamenobu was born on January 18, 1550, as the adopted son and heir of Ōura Tamenori, a retainer of the Nanbu clan, based at Sannohe Castle.

He made attempts to reach Hideyoshi overland in 1586, 1587, and 1588, but he was blocked each time by hostile forces in the territories to the south of Tsugaru.

In 1589, Tamenobu approached Ishida Mitsunari with gifts of horses and falcons for Toyotomi Hideyoshi, and asked for formal recognition as daimyō over his existing holdings (i.e. the three Tsugaru districts of Hiraga, Hanawa and Inaka of far northwestern Mutsu Province).

Nanbu Nobunao, supported by Maeda Toshiie declared Tamenobu to be a rebellious vassal who had seized the Tsugaru region illegally, and demanded his punishment.

Tamenobu was supported by Ishida Mitsunari, Hashiba Hidetsugu and Oda Nobukatsu and as he had pledged fealty to Hideyoshi earlier than Nanbu Nobunao, his claims to Tsugaru were officially recognised.

With his third son, Tsugaru Nobuhira, he participated in the Battle of Sekigahara as part of the Eastern Army under Tokugawa Ieyasu.

His eldest son, Tsugaru Nobutake, was serving Toyotomi Hideyori at the time as a page in Osaka Castle.

Tamenobu also feared a rebellion within his domains during his absence and had the suspected leader, Morioka Nobumoto, put to death before his departure.

In 1607, Tamenobu received word that his eldest son, Nobutatsu, was ill in Kyoto and set out from Hirosaki to visit him.