Fujimaru Katsutoshi served as a bushō during the Sengoku and Azuchi-Momoyama periods. He was a retainer of the Uesugi clan.
Katsutoshi originated from Kaga Province. Based at the Akao fortress in the Enuma District, he participated in the Kaga Ikkō-ikki, a nearly century-long uprising by followers of the Hongan Temple in Kaga that ran from 1488 to 1580.
In 1582, at the Siege of Uozu Castle, Katsutoshi fought valiantly as the commander in charge of the castle but, during an assault by Shibata Katsuie (a senior retainer of the Oda clan), took his own life.