He was the General Commander (総長, Sōchō) of the Shinsengumi, a special police force in Kyoto during the late Edo period.
Yamanami was trained under Chiba Shusaku Narimasa, the founder of the Hokushin Itto-ryu, and attained Menkyo Kaiden (license of total transmission) sometime before 1860.
In 1863, Yamanami, Kondo, and other members of the Shieikan joined the Rōshigumi, the military unit being sent to Kyoto by the Tokugawa Shogunate.
Yamanami served as a vice-commander, alongside Hijikata Toshizō after Niimi Nishiki was demoted for instigating a vicious street brawl with sumo wrestlers in Kyoto.
Another theory is Yamanami lost hope about Shogunate's future and was disillusioned about the political decisions of Tokugawa Yoshinobu, but when forced to choose between his friends and justice, he decided to commit an honorable suicide and escape scandal.
According to most sources, Yamanami's vexation was exacerbated sometime early in 1865, when Kondo and Hijikata, unhappy with their cramped headquarters at Mibu, decided to move to a more spacious location at Nishihonganji Temple in the southwest of the city.
He composed a farewell letter explaining the reasons he could no longer, in good conscience, risk his life under Kondo's command.
In addition, Hillsborough's theorizing of a rivalry between Yamanami and Hijikata in Shimosawa Kan's Shinsengumi Shimatsuki is categorized as historical fiction.