Born a son of Imagawa Ujichika, military governor of Suruga (Shizuoka). Not being the heir, he entered a temple as a small child and was raised as a monk.
Around this time he studied Zen and learning at Kyoto temples with his teacher Taigen Sessai, who later supported the Imagawa as Yoshimoto's strategist and political adviser.
His elder brother Ujiteru died suddenly, sparking a succession dispute. Yoshimoto defeated his half-brother Genkō Etan (Hanakura Rebellion) and became head of the Imagawa at 17.
He married a daughter of Takeda Nobutora of Kai and allied with the Takeda, which angered the Hōjō of Sagami and led to war with them.
Expanding into Mikawa, he defeated Oda Nobuhide of Owari at Azukizaka. The next year he took Takechiyo (later Tokugawa Ieyasu) of the Matsudaira as a hostage at Sunpu.
He added new articles to his father's domain law, the Imagawa Kana Mokuroku, declaring that he governed by his own power rather than the shogun's orders—a clear statement of independence as a Sengoku daimyō.
Exchanging daughters in marriage with Takeda Shingen and Hōjō Ujiyasu, he formed a three-way alliance. Secure at his back, he could turn his strength westward.
His teacher and trusted adviser Taigen Sessai died. Yoshimoto welcomed many Kyoto courtiers to Sunpu, where capital culture such as waka and kemari flourished.
He invaded Owari with a large army, but while resting at Okehazama he was surprised by Oda Nobunaga and lost his life. Ruler of Suruga, Tōtōmi and Mikawa, he had been called "the finest archer of the Tōkaidō".
Taigen SessaiOda NobunagaTokugawa IeyasuSakai TadatsuguAshikaga YoshiteruImagawa UjizaneHonda MasanobuSakakibara Yasumasa
Francis XavierŌuchi YoshitakaMatsunaga HisahideHōjō UjiyasuImai SōkyūTakeda ShingenSue Harukata (Takafusa)Sen no Rikyū
People of the Sengoku/Azuchi-Momoyama period ・ People by period
Based on facts found in textbooks and biographies. Uncertain points are marked as such.