In 1568, when Oda Nobunaga marched his armies, Tomomasa and Katsumasa under Miyoshi clan battled against him. However, they were not equal to him by their nature. They surrendered and served Nobunaga. In 1570, when Ikeda clan's infighting happened, Katsumasa who was the family head was purged. Because of that, Tomomasa succeeded to a house. In 1571, he held secret communication with Miyoshi Nagayasu, Miyoshi Masayasu and Iwanari Tomomichi, and betrayed Nobunaga. They defeated Wada Koremasa and killed him.
He served Tokugawa Ieyasu and was given 5,000 koku after Hideyoshi died. After Tomomasa died, his son, Ikeda Shigenobu succeeded to a house. However, his domain was seized by the shogunate.