During his life Kamatari was the leader of Shinto Rituals (jinji no haku) though it was during this time that Buddhism was growing in popularity at court.1
In 552, the Nakatomi and Mononobe fought unsuccesfully to stop Buddhism being introduced, the Soga winning out who favored Buddhism.2
By now the Soga Clan had grow vastly in power and so Prince Naka no Ōe enlisted the help of Kamatari to try and destory the Soga Clan. This led to a coup in 645 where Soga no Iruka was killed and Soga no Emishi committed suicide.
Legends say the plan to eradicate the Soga were made in a wisteria arbor (fujiwara).
After this Emperor Kōtoku designated Naka no Ōe as his heir and made Kamatari Inner Minister (uchi-tsuomo), a position later called Naidaijin from 669. Due to this Kamatari was the first to hold the position of Naidaijin (Minister of Domestic Affairs).
Kamatari launched a program of reforms with Naka no Ōe in 645 called the Taika Reforms to reinforce Imperial Authority.2