Aoyama Munekatsu served as a bushō and daimyō during the Azuchi-Momoyama and early Edo periods.  He held the title of Junior Fifth Rank (Lower) and Assistant Officer of Palace Repairs.

Munekatsu was born in 1561.  First, he served Niwa Nagahide.  After the death of Nagahide in 1585, he became a retainer of Toyotomi Hideyoshi and was selected to be a member of an elite cavalry division known as the kiboroshū for the yellow capes worn in battle to deflect arrows and other objects that may be hurled at them.  Munekatsu was granted a fief of 20,000 koku in Echizen Province.  In 1587, he participated in the Kyūshū Pacification.  Owing to his contributions for the construction of Fushimi Castle, in 1598, he was awarded 46,000 koku in Maruoka and Maruoka Castle in Echizen.  Munekatsu was then conferred the title of Junior Fifth Rank (Lower) and Assistant Office of Palace Repairs.  At this same time, it is surmised that he was permitted to use the Toyotomi surname.

In 1600, at the Battle of Sekigahara, Munekatsu joined the Western Army and fought against Maeda Toshinaga of the Eastern Army.  Owing to the defeat of the Western Army, after the war, he was removed from his position.

Thereafter, he served Niwa Nagashige, the son of his prior lord, Niwa Nagahide.  His son, Nagakatsu, was permitted to adopt the Niwa surname and was treated as a family member.  His descendants served as senior retainers of the Nihonmatsu domain until the end of the Edo period.