Very little is known about the actual life of Yagyū Mitsuyoshi as the official records of his life are very sparse. Yagyū Jūbē Mitsuyoshi (born 1607) grew up in his family's ancestral lands, Yagyū no Sato, now in Nara. He was the son of Yagyū Tajima no Kami Munenori, master swordsman of the Tokugawa shōguns.
Munenori fought for the first Tokugawa shōgun, Tokugawa Ieyasu, at the Battle of Sekigahara, expanding the shōgun's territory. For his efforts, Munenori was made the shōgun's sword instructor and a minor daimyō (provincial ruler), by extending his family hereditary domain up to 10,000 koku.
In 1616, Mitsuyoshi became an attendant in the court of the second Tokugawa Shōgun, Tokugawa Hidetada and became a sword instructor for the third Tokugawa Shōgun, Tokugawa Iemitsu, occasionally filling his father's role. Records of Yagyū Jūbē Mitsuyoshi, however, do not appear again until 1631, when Jūbē, by now regarded as the best swordsman from the Yagyū clan, is summarily and inexplicably dismissed by the Shōgun either due to Jūbē's boldness and brashness or his decision to embark on a Warrior's Pilgrimage (武者修行, Musha Shugyō).
His whereabouts are then unknown over the next twelve years—even the Yagyū clan's secret chronicles, which contained lengthy passages on numerous members, has little solid information on Jūbē—until Yagyū Jūbē reappears at the age of 36 at a demonstration of swordsmanship in front of the Shōgun. Following this exhibition, Jūbē was reinstated and serves for a short time as a government-inspector (御所印判, Gosho Inban), taking control over his father's lands until Yagyū Tajima no Kami Munenori's death in 1646.
Jūbē also authored a treatise known as Tsuki no Shō (月之抄) or The Art of Looking at the Moon outlining his school of swordsmanship as well as teachings influenced by the monk Takuan Sōhō who was a friend of his father's. In this work he briefly provides hints on his whereabouts during his absence from Edo Castle from 1631 to 1643 – traveling the countryside in perfecting his skills.
After residing in Edo for several years after his father's death, Jūbē left his government duties and returned to his home village where he died in early 1650 under uncertain circumstances. Some accounts say he died of a heart attack; others say he died while falcon hunting; some during fishing, while still others presume he was assassinated by his half-brother Yagyū Tomonori's attendants.
Jūbē was laid to rest in his home village of Yagyu behind the family temple of Hotojukuji alongside his father and brother. In keeping with tradition, Yagyū Jūbē was buried alongside his grandfather, Yagyū Munetoshi, and was survived by two daughters and his brother and successor Yagyū Munefuyu. Jūbē was given the Buddhist posthumous name of Sohgo.