In 1863, Harada, together with Kondō and others associated with the Shieikan, joined Kiyokawa Hachirō's
Rōshigumi and departed for
Kyoto. Shortly after reaching Kyoto, the Rōshigumi was disbanded and most of its members returned to Edo. Harada, Kondō,
Serizawa Kamo and several others remained behind and formed the core of the group known as
Mibu Rōshigumi, which later became the Shinsengumi. Later, Harada became the Captain of the Shinsengumi tenth Unit. He was trained briefly under a dojo run by
Tani Sanjūrō, whom he introduced into the Shinsengumi. In 1865, Tani became the seventh Unit Captain. In Kyoto, Harada married a local woman named , and briefly had a private family residence near the Shinsengumi headquarters at Nishi-Honganji. At one time he was accused (by former Shinsengumi member
Itō Kashitarō) as one of the assassins of the
Sakamoto Ryōma and
Nakaoka Shintarō who were murdered on December 10, 1867. The truth behind the incident remains unclear, but according to the confession of the Tokugawa retainer
Imai Nobuo later in 1870, the assassins were men of the
Mimawarigumi (another Tokugawa-affiliated unit) under the
hatamoto Sasaki Tadasaburō. Later on December 13, 1867, he,
Nagakura Shinpachi and several Shinsengumi members were involved in the ambush of Itō Kashitarō's
Goryō Eji Kōdai-ji faction during the
Aburanokōji incident. In January 1868, Harada, together with the rest of the Shinsengumi, fought at the
Battle of Toba–Fushimi against the Imperial forces. He and his family subsequently left the Kyoto region for
Edo. In March, the Shinsengumi was renamed to and advanced on
Kai Province, and fought at the
Battle of Kōshū-Katsunuma, however, the unit was defeated and forced to retreat back to Edo. In the wake of this defeat, Harada and
Nagakura Shinpachi left the Kōyō Chinbutai after disagreements with Kondō and Hijikata. According to Nagakura's version of events, Kondō wanted the surviving men to become his retainers; Nagakura, Harada, and a few others staunchly refused. Nagakura and Harada, taking with them some other Shinsengumi members, joined with a group of former Tokugawa retainers to form a new unit, the
Seiheitai. Seiheitai left Edo shortly after Edo Castle's surrender, and headed north, hoping to take part in the fighting that was moving northward, toward
Aizu. ==Death==