Little is known of Takeda Kanryuusai's life before joining the Shinsengumi, but he was likely involved in academics and medicine. His sword style was most likely Hokushin Ittō-ryū, although he does not appear to have been very skilled. He was close to the influential loyalist Hirano Kuniomi. However, he was too outspoken an advocate of sonno joi and was arrested. He escaped imprisonment in 1863 and fled to Kyoto to join the Shinsengumi.
Takeda was assigned to assist in the arrest of Furutaka Shuntaro (also known as Masuya Kiemon), which lead to the Ikedaya Affair. He was a member of Kondo's group and helped to secure the perimeter of Ikeda-ya. Takeda participated in the indoor battle after the arrival of Hijikata's group, bringing down the ceiling and killing a Tosa ronin. He received a 20 ryou bonus for valor in combat. Soon after, he was sent as an officer to the Akebono Restaurant incident, in which an Aizu retainer accidentally killed a Nagato retainer.
When Nagakura Shinpachi and others petitioned the Aizu clan on account of Kondou's allegedly despotic leadership, Takeda strived to mediate between the two sides. After that, he turned to military affairs such as increasing the ranks of the Shinsengumi. In September he accompanied Kondo to Edo as his secretary; in November, he went to Nagato as a military advisor. He outranked military advisor Ito Kashitaro at the time. However, the Shinsengumi were beginning to adopt more Western military techniques based on the French army by the time of Ito Kashitaro's enlistment, which rendered Takeda's Koushuu style obsolete. However, a clever appeal to Kondou earned Takeda the position of fifth Unit Captain in 1865. He also taught strategy and tactics.
But Itou Kashitarou's excellence in academics and martial arts was not ignored by Kondo, no matter how fond he was of his sycophant, Takeda. Takeda was left off an 1866 business trip to Hiroshima in favor of the other military advisor. In desperation, he sought whatever allies he could.
There are conflicting accounts of how and when Takeda was killed. The first is that he was assassinated on September 28th, Keiou 2 (November 5th, 1866) on his way back from Izumo. He was making his way across the Zenitori Bridge of the Taketa Highway in Fushimi when he was confronted by Saito Hajime and Shinohara Tainoshin. Saitou Hajime is often credited with the killing, although Shinohara is said to be the true assassin. The other story is that he was not murdered until June 22nd, Keiou 3 (July 23, 1867), on his way home along that highway from a farewell party organised by Kondo. He had obtained permission to leave, but the Shinsengumi secretly plotted against him. He may have also attempted to join Itou's group at this time, but was turned down. He then intended to join Satsuma. Saitou, and sometimes Shinohara, are usually credited in this version of the assassination as well, but they had both left the Shinsengumi months earlier as a part of Itou's group. There is much unresolved confusion over when exactly Takeda left the Shinsengumi and when his treachery was discovered. The 1867 date is more widely used.
Rurouni Kenshin author Nobuhiro Watsuki cites Takeda Kanryūsai as the inspiration for a character by the name of Takeda Kanryū, who appears for a few chapters in the manga, as well as in the television series of the same name.