The Yanagisawa house traced descent to the "Kai-Genji," the branch of the Minamoto clan which had been enfeoffed with the province of Kai in the eleventh century.

Yoshiyasu served Tsunayoshi from an early age, becoming his Wakashū and eventually rose to the position of soba yōnin.^{[citation needed]} He was the daimyō of the Kawagoe han, and later of the Kōfu han in Kai Province, a signature honour as it has been the fief held by Tsunayoshi before becoming shōgun, and of Ienobu, his heir apparent, as well as having an historic familial connection; he retired in 1709.^{[citation needed]} Having previously been named Yasuakira, he received a kanji from the name of the shōgun, and came to call himself Yoshiyasu.^{[citation needed]} He built Rikugien Garden, a traditional Japanese garden, in 1695. He had an adopted son named Yanagisawa Yoshisato by Tokugawa Tsunayoshi with Yoshiyasu's concubine, Sumeko.^{[clarification needed]}

Yanagisawa played a pivotal role in the matter of the forty-seven rōnin.^{[citation needed]}

Yanagisawa is the subject the diary memoir of his concubine Ōgimachi Machiko (正親町町子, 1675 - 1724), Matsukage no nikki ('In the Shelter of the Pine'), which gives a detailed account of Yoshiyasu's glory during the period 1685-1709 modelled on the Eiga Monogatari and in a writing style inspired by The Tale of Genji. More than 36 hand-copied manuscripts survive to the present day. An English translation appeared in 2021.

Yanagisawa appears as a character in most of the novels by American mystery writer Laura Joh Rowland set in Genroku-era Japan as the antagonist to the books' main character Sano Ichiro.^{[citation needed]} Rowland's chronology differs from history by having Yanagisawa exiled in disgrace in 1694 and being replaced by Sano as Tsunayoshi's chief advisor, only to return from exile later in the series.^{[citation needed]} Other details of Yanagisawa's life, however, are portrayed fairly accurately, including his relationship to the shōgun.^{[citation needed]}

• Samurai
• Shudō

• Bodart-Bailey, Beatrice. (1980). Yanagisawa Yoshiyasu: a Reappraisal. Canberra: Australian National University. OCLC 222149819
• Nussbaum, Louis Frédéric and Käthe Roth. (2005). Japan Encyclopedia. Cambridge: Harvard University Press. ISBN 978-0-674-01753-5; OCLC 48943301