Born in 1538 as son of a Tokugawa retainer in Mikawa. In his youth he joined an Ikko-ikki rebellion and fled Ieyasu's service, wandering for years before being forgiven and returning. His exceptional intelligence made him Ieyasu's most trusted advisor. At Sekigahara he directed strategy at Ieyasu's side without taking the field himself, playing a key behind-the-scenes role in the Eastern victory. After the establishment of the shogunate he became roju (senior councilor), contributing enormously to building the bakuhan system. Contrasted with the martial Honda Tadakatsu, he was known as a strategist—the two called "the two Hondas." He helped engineer the Hoko-ji bell inscription affair to trap the Toyotomi. He died in 1616 at age 79.

Rich in strategic intelligence, preferring to solve problems through cunning and persuasion over force. Taciturn and calm in judgment, he earned Ieyasu's full trust. The experience of being forgiven for past rebellion is said to have deepened his ultimate loyalty.

Honda Masanobu's stratagems played an indispensable role in establishing Tokugawa rule. His involvement in the series of maneuvers that brought down the Toyotomi continues to generate divided historical assessments.