Born in 1793 as the second son of the 11th shogun Ienari. He became the 12th shogun in 1837 at age 45—the oldest accession in Tokugawa history. His father Ienari retained real power as retired shogun, so Ieyoshi's actual rule began only after Ienari's death in 1841. To restore finances ruined by his father, he appointed Mizuno Tadakuni as senior councilor and launched the 'Tenpo Reforms'—strict austerity and morality laws. But the Agechi-rei (land requisition order) provoked fierce opposition, Tadakuni was dismissed, and the reforms collapsed. He then promoted young Abe Masahiro as senior councilor. In June 1853, Perry's Black Ships arrived at Uraga, but Ieyoshi was already on his deathbed. He learned of Perry's arrival and died just 6 days later on June 22, at age 61.

Gentle and cautious in temperament. His years of patience under his father's shadow governance cultivated endurance. He had the will for reform but limited ability to execute.

The 'shogun on the eve of the Black Ships' who died the same year Perry arrived. Though the Tenpo Reforms failed, his appointment of Abe Masahiro paved the way for the opening of Japan. He symbolizes a turning point between eras.