Mitsuharu was from Mino and at first a retainer of the Toki, and then the Saitô. He later joined Nobunaga and served him in a largely diplomatic capacity. He was awarded land in Echizen in 1575 and became one of the 'Echizen Triumvirs' (Sanninshu) along with Maeda Toshiie and Sassa Narimasa.