Mōri Yoshikatsu served as a bushō during the Sengoku and Azuchi-Momoyama periods.  He was a retainer of the Oda clan.

Yoshikatsu is said to have originated from Owari Province but this is not certain.  He served as an umamawari, or member of the cavalry division, for Oda Nobunaga.  There is also a theory that he was a koshō, or assistant to senior bushō.  He first used the name of Shinsuke.

In 1560, during the Battle of Okehazama, he assisted Hattori Koheita (Hattori Kazutada) who sustained injuries as the first one to slash his way toward Imagawa Yoshimoto, a sengoku daimyō and the eleventh head of the Imagawa clan.  Shinsuke (Yoshikatsu) gained renown for killing Yoshimoto in the battle.  The authenticated biography of Oda Nobunaga known as the Shinchō-kōki states it was rumored that this was providence owing to the protection of Mōri Hideyori (the young lord and natural son of Shiba Yoshimune) by his adoptive father, Mōri Jūrō.  When Shinsuke attacked Yoshimoto, there is an unsubstantiated story that Yoshimoto bit-off one of his fingers.  After the Battle of Okehazama, he changed his name from Shinsuke to Yoshikatsu while adopting the common name of Shinzaemon.

Nobunaga fielded an elite cavalry known as the horoshū who rode with brightly colored canopies to deflect arrows or other objects hurled at them in battle.  Yoshikatsu’s name appears among the members of the kurohoroshū displaying black canopies.

After Nobunaga marched to Kyōto, in 1569, Yoshikatsu participated in the Siege of Ōkawachi Castle against Kitabatake Tomonori.  As a close associate of Nobunaga, Yoshikatsu with a group of retainers known as the sakukiwamawari-banshū having responsibility to defend the main base.  Yoshikatsu served primarily as an official in the Oda administration so his seal and signature are found on many letters and ancillary documents.

In 1582, Yoshikatsu accompanied Nobunaga during the Invasion of Kōshū against the Takeda clan.  While stationed in Suwa, he received gifts from the Daijōin (sub-temple) of the Kōfuku Temple.

On 6/2 of Tenshō 10 (1582), Nobunaga died in a coup d’ètat led by Akechi Mitsuhide in Kyōto.  This is known as the Honnō Temple Incident.  At the time of this event, Yoshikatsu was staying in the capital.  In an effort to protect Nobunaga’s lineal heir, Oda Nobutada, he holed-up in the Nijō palace.  Yoshikatsu, together with Nobutada, was subsequently killed in action.