Kuninaga Tajimi was born in Mino Province, Gifu Prefecture. He was the son of Kunizumi.
When Emperor Godaigo planned to overthrow the Shogunate he and Yorikane Toki, his relative, at the advice of Sumitomo He, sneaked into Kyoto to participate in the plan (1324). Under cover of the confusion at the festival of the Kitano Shrine in September that year, he attempted to attack the Shogunate police office at Rokuhara. The attempt was frustrated because Yoriharu Funaki, his relative, informed the Shogunate. He was besieged by Shogunate troops in Shijo, Kyoto, and killed himself.