Niwa Ujikatsu served as a bushō during the Sengoku and Azuchi-Momoyama periods.  He was a retainer of the Oda caln and served as the lord of Iwasaki Castle in Owari Province.

The ancestors of Ujikatsu’s family from Iwaski were the Isshiki-Niwa, a branch of the Ashikaga clan.  Ujikatsu was not a blood relative of Niwa Nagahide, another senior commander of the Oda who came from the Kodama-Niwa clan.

In 1555, a retainer of Oda Nobutsugu (lord of Moriyama Castle) named Suga Saizō killed Nobunaga’s younger brother, Hidetaka.  Fearing retribution from Nobunaga, Nobutsugu fled and his retainers, including Ujikatsu, took refuge in Moriyama Castle.  Ujikatsu also appears in connection with a rebellion by an elder retainer of Nobutsugu named Tsunoda Shingo.  Thereafter, he became a direct retainer of Nobunaga.

In 1569, Ujikatsu participated in the Battle of Okawachi Castle; and in the sixth month of 1570, the Battle at Ane River in Ōmi Province, followed soon thereafter by the Battle of Noda-Fukushima Castle, and then on to Sakamoto after receiving news that the Azai and Asakura had raised arms against the Oda.  He then joined in the attack on Mount Hiei and, in 1575, the excursion into Echizen.  In the second month of 1577, Ujikatsu further contributed in battles against the Saika clan in Kii Province. 

In 1580, when Nobunaga visited Mt. Iba to engage in his past-time of falconry, Ujikatsu’s men were extracting large boulders for construction, and one of the subordinates dropped a boulder on the road in front of Nobunaga.  Enraged, Nobunaga slayed one of the workman on the site.  Later that year, Nobunaga suddenly banished Ujikatsu, along with fellow retainers Hayashi Hidesada and Andō Morinari.  

Thereafter, Ujikatsu roamed from place to place, and after the death of Nobunaga, returned to Bōjimoto Castle, the base of his second son, Ujishige, for the remainder of his life.  Ujikatsu died in 1597 at the age of seventy-five.