chief adviser to Tokugawa Ieyoshi (reigned 1837–53), 12th Tokugawa shogun, or military dictator, of Japan. Mizuno was responsible for the Tempō reforms, the Tokugawa shogunate's final effort to halt the growing social and economic decline that was undermining its rule.

The son of a prominent feudal lord, Mizuno in 1828 was appointed tutor to the Tokugawa heir apparent, Ieyoshi. Although Mizuno was elevated to the position of chief shogunal adviser in 1834, he exercised little power until Tokugawa Ienari (reigned 1787–1837), the 11th shogun, finally died three years later and Ieyoshi succeeded him. Thereafter, until his dismissal from office in 1843, Mizuno virtually controlled the government.

Mizuno came to power at a time when popular unrest was sweeping the country after almost a decade of serious famines. His rise also coincided with China's defeat by Great Britain in the trading dispute known as the Opium War (1839–42); and Mizuno recognized that, if Japan did not solve its internal problems, it would be helpless in the face of the inevitable Western encroachment. To this end, he made a vain effort to reinstate the simple martial virtues of the early Tokugawa period. He insisted on personal and governmental frugality, introducing sumptuary laws that went to unenforceable extremes. In an attempt to hamper the growing trade economy, which he considered frivolous, Mizuno canceled all debts owed by noblemen to members of the middle class, abolished many of the merchant guilds licensed by his predecessors, and ordered peasants who had migrated to the cities to return to the countryside. A program to appropriate vassals' domains near Edo and Ōsaka aroused much opposition, and Mizuno's measures became so unpopular that the shogun had to dismiss him.