Lifespan: Tenbun 19 (1550) to 3/19 of Keichō 6 (1601)
Rank: bushō, daimyō
Lord: Oda Nobunaga → Oda Nobutada → Oda Nobukatsu → Tokugawa Ieyasu → Oda Nobukatsu → Toyotomi Hidetsugu → Tokugawa Ieyasu
Father: Niwa Ujikatsu
Siblings: Ujitsugu, Ujishige, sister (wife of Katō Tadakage)
Wife: [Formal] Daughter of Suzuki Shigenobu, [Second] Daughter of Katō Tadakage
Children: Ujisuke, Ujinobu, Sassa Heizaemon (Masamoto)
Niwa Ujitsugu served as a bushō and daimyō during the Sengoku and Azuchi-Momoyama periods. He was the first head of the Ujitsugu branch of the Niwa family.
In 1550, Ujitsugu was born as the eldest son of Niwa Ujikatsu in Iwasaki in Owari Province. Ujitsugu succeeded his father and served Oda Nobunaga. In 1580, Ujikatsu incurred the wrath of Nobunaga and was ousted, but this incident did not appear to affect Ujitsugu. Thereafter, he served as a retainer of Oda Nobutada. In 1582, Ujitsugu joined Kiso Yoshimasa and Oda Nagamasu as members of Nobutada’s division to invade the Takeda territory in the Conquest of Kōshū.
After Oda Nobunaga died on 6/2 of 1582 at the Honnō Temple Incident, Ujikatsu served Nobunaga’s second son, Oda Nobukatsu. Thereafter, he came into conflict with Nobukatsu so, in 1583, he became a retainer of Tokugawa Ieyasu. In 1584, at the Battle of Komaki-Nagakute, he had his younger brother, Niwa Ujishige, protect Iwasaki Castle while Ujitsugu made contributions on the battlefield in Komaki on the side of Ieyasu. At this time, however, Ujishige was subject to a fierce attack by the forces of Ikeda Tsuneoki and Mori Nagayoshi, dying at the Battle of Iwasaki Castle.
Later, through the mediation of Ieyasu, Ujitsugu served Nobukatsu again and was awarded a fief of 7,000 koku in Ise Province. However, after the Conquest of Odawara, Nobukatsu was removed from his position, so Ujitsugu pleaded with Toyotomi Hideyoshi to return to the service of Ieyasu, but Hideyoshi assigned him to Toyotomi Hidetsugu instead. At this time, his eldest son, Niwa Ujisuke, was assigned to Ieyasu. On 9/15 of Keichō 5 (1600), at the Battle of Sekigahara, Ujitsugu joined the Eastern Army and was ordered to reinforce the defenses at Iwasaki Castle – a strategic location between Owari and Mikawa provinces. Upon orders of Ieyasu, he dispatched several hundred laborers to strengthen defenses at Tsumagi Castle (defended by Tsumaki Yoritada) to prepare for an attack by Tamaru Naomasa (the lord of Iwamura Castle) who was allied with Ishida Mitsunari of the Western Army. Tamaru Naomasa himself was defending Ōsaka Castle at the time. Subsequently, owing to his contributions at the Battle of Sekigahara, Ujitsugu was awarded a fief of 10,000 koku in Ibo in Mikawa and became the first head of the domain.
Ujitsugu died on 3/19 of Keichō 6 (1601) at the age of fifty-two (or fifty-three) and was succeeded by his second son, Niwa Ujinobu.
Ujitsugu possessed a spear with a long blade manufactured in the mid-sixteenth century in Mino Province inscribed by Masatoshi from the Sengo (Muramasa) school of Ise Province. When stabbing the enemy, the blade pierced the body armor and went through to the stone wall behind his opponent, so thereafter it was referred to as the Stone-Piecing Spear.