Matsunaga Hisamichi served as a bushō during the Sengoku and Azuchi-Momoyama periods.  He was the eldest son of Matsunaga Hisahide.

In 1543, Hisamichi was born as the eldest son of Matsunaga Hisahide, a retainer of the Miyoshi clan.  He soon followed after his father.  In 1563, Hisahide transferred headship of the clan to Hisamichi and Hisamichi also became the lord of Tamonyama Castle in Yamato.  In the twelfth month of the same year, he was invested with the title of Junior Fifth Rank (Lower) and Assistant Captain of Outer Palace Guards of the Right Division, an official appointment of the bakufu.  On 6/22 of Eiroku 7 (1564), he followed Miyoshi Yoshitsugu, the nephew and adopted heir of his lord, Miyoshi Nagayoshi, and marched to Kyōto.  On 6/23, he met Ashikaga Yoshiteru, the thirteenth shōgun of the Muromachi bakufu.  In 1565, in lieu of Hisahide, Hisamichi joined forces with the Miyoshi Group of Three and Yoshitsugu to assassinate Yoshiteru at the Nijō palace in Kyōto in an event known as the Eiroku Incident.

Beginning from that same year, internal conflicts erupted between his father and the Miyoshi Group of Three.  From the fifth month of 1566, as Hisahide went into hiding, Hisamichi guarded Tamonyama Castle.  Until his father returned in the fourth month of 1567, Hisamichi fought against Tsutsui Junkei, a supporter of the Miyoshi Group of Three, in Yamato.  In 1568, when Oda Nobunaga backed Ashikaga Yoshiaki (the younger brother of Ashikaga Yoshiteru) and marched upon Kyōto, Hisamichi and his father surrendered to Nobunaga and received recognition of the rights to their territory in Yamato.  Later, after Yoshiaki led the formation of an encirclement campaign to oppose Nobunaga, Hisamichi and his father sided with Yoshiaki in a revolt against Nobunaga.  In 1573, after an attack by Oda forces against Tamonyama Castle, Hisamichi joined his father by surrendering again.

In the seventh month of 1575, Hisamichi received as his wife the daughter of Tōichi Tōkatsu named Goryō and moved to Ryūōzan Castle, but, upon orders of Harada Naomasa (also known as Ban Naomasa, the military governor of Yamato), in the third month of 1576, attacked and toppled Tōichi Castle which was the base of his wife’s uncle named Tōichi Tōnaga.  In the fifth month, Hisamichi participated in attacks against the Ishiyama-Hongan Temple known as the Battle of Ishiyama.  On 5/3 of Tenshō 4 (1576), Naomasa was killed in action at the Battle of Tennō Temple,  and there were unfounded rumors that Hisamichi had also been killed.

In the tenth month of 1577, when his father, Hisahide, rebelled a second time against Oda Nobunga, he followed him and opposed Nobunaga.  At the Siege of Shigisan Castle, however, after setting the castle on fire, both of them took their own lives.  There is an alternate theory that he fled Shigisan Castle and was killed by field soldiers while en route to Ōsaka.  During the Siege of Shigisan Castle, two of his sons who had earlier been tendered as hostages to the Oda were paraded around Kyōto and then executed at Rokujō-gawara along the Kamo River.  The boys were said to have been twelve and fourteen years old.

Descendants

According to one theory, he had a son named Hikobei (Ichimaru), and his descendants included a vice-admiral in the navy (Matsunaga Sadaichi) and a lieutenant in the navy (Matsunaga Ichirō).