Koremasa was the son of Wada Koresuke (d. 1546). He was a supporter of the Ashikaga shogunate who aided Ashikaga Yoshiaki following the murder of the shôgun Yoshiteru in 1565. He continued to serve the Ashikaga under the auspices of the Oda and was essential in securing Luis Frois an audience with Nobunaga in 1569. He supported the Takayama clan and was later killed fighting with Araki Murashige in their defense.