Godai Tomoyasu served as a bushō during the Sengoku and early Edo periods.  He was a retainer of the Shimazu clan of Satsuma Province.

Tomoyasu came from an illegitimate branch of the Shūin clan who served as hereditary Shintō priests of the Nitta-Hachiman Shrine in Satsuma.  The family adopted the Godai surname from the time that the first-generation head of the family, Koremune no Yasutada (the son of Koremune no Yasutomo from the Kamakura period), served as the head priest of the Godai Temple.

In 1568, Tomoyasu was born as the lineal heir of Godai Tomoyoshi, a chief retainer of Shimazu Yoshihiro.  In 1590, when Shimazu Hisayasu (the second son of Shimazu Yoshihiro), marched for the Conquest of Odawara, Tomoyasu and his father were included among sixteen cavalry members accompanying Hisayasu.  Tomoyasu also accompanied Hisayasu for the Bunroku Campaign on the Korean Peninsula.  On 9/8 of Bunroku 2 (1593), he died of illness on Geoje Island in Korea.  He was twenty-one years old.  Three individuals martyred themselves after he died while Tomoyasu brought his remains back to Japan.

To pray for the soul of Hisayasu, Tomoyasu made a pilgrimage across Japan, made votive offerings of sixty-six scriptures, and returned to his residence in Fushimi.  He was then ordered by Hisayasu’s younger brother, Shimazu Tadatsune, to join another crossing to the Korean Peninsula.

In 1598, soon after the death of Toyotomi Hideyoshi, a decision was made to withdraw the Japanese army from Korea.  After the Battle of Noryang, the last major battle of the Japanese invasions of Korea fought between the Japanese navy and the combined fleets of the Joseon and Ming navies, some of those serving safely escaped while over 500 Shimazu forces including Kabayama Hisataka drifted on the tide and were compelled to hole-up at a Japanese fortress on Namhae Island.  This contingent was subsequently encircled by enemy vessels.  In a bid to rescue them, Yoshihiro secretly planned to send a ship to pick-up the men and dispatched Tomoyasu, along with Ise Sadamasa, Arima Shigezumi, and Samejima Munetoshi, to inform them.  Tomoyasu headed toward Namhae in a small boat amidst the enemy vessels besieging the stranded forces.  After informing Hisataka of the plans, he safely returned to base.  Hisataka and the contingent of 500 men then escaped to 興善 Island in Korean waters.  Later, Tomoyasu was awarded 100 koku for his contributions.

After returning from Korea, Tomoyasu as charged with guarding Kakutō Castle and served as lord of the manor.

Tomoyasu died in 1642.  His eldest son, Godai Tomosada, died in 1631, without an heir so the headship of the clan was inherited by his second son, Godai Tomomitsu.