Toichi Tookatsu succeeded his father Toichi Tootada as head of the Toichi Clan of Yamato in 1545 at a young age. In 1559, when Miyoshi Nagayoshi became the real power in the capital and sent his vassal Matsunaga Hisahide to take Yamato, Tookatsu formed an alliance with Tsutsui Junkei to resist him. However, his daughter was taken hostage, and Tookatsu submitted to Hisahide.

A brief peaceful interlude dissolved into further conflict when Miyoshi Nagayoshi and Hisahide began battling the Miyoshi Triumvirate. Tsutsui Junkei took the side of the Triumvirate, and the Toichi Clan split between those who wanted to join Hisahide and those who wanted side with the Tsutsui Clan. The Akiyama Clan, who had joined with Hisahide, invaded Toichi terrority in 1568. Unable to defend against the attack, Tookatsu abandoned Ryuuouzan Castle and fled to Toichi Castle.

Hisahide's power and influence grew rapidly under Oda Nobunaga, and Tookatsu turned to him once more. However, he suddenly died of illness the following year without a son to succeed him.