Saruwatari Nobumitsu was son of Saruwatari Nobusuke and a retainer of the Shimazu Clan. He held Kaseda and Hazuki as his fiefdoms and was extolled as a brave warrior. He fought in the invasion of Higo and led 1,000 soldiers (out of 6,000 - 8,000) in the Battle of Okitanawate of May 3, 1584 against the Ryuuzouji army. His heir Yajirou was killed in the battle.

He was killed in 1587 during the Battle of Nejirozaka during Toyotomi Hideyoshi's pacification of Kyuushuu.