Ujiie Naomasa served as a bushō during the Sengoku and Azuchi-Momoyama periods.  He was the thirteenth head of the Ujiie clan.

The Ujiie were an illegitimate branch of the Utsunomiya clan descended from the Fujiwara-Hokke.  Naomasa was born as the eldest son of Ujiie Naomoto (later known as Bokuzen, the lord of Ōgaki Castle) who, along with Inaba Yoshimichi and Andō Morinari, was one of the Western Mino Group of Three.

Initially, Naomasa served the Mino-Saitō clan but then surrendered to Oda Nobunaga.  In 1571, during the Nagashima Ikkō-ikki (attacks by Oda Nobunaga against followers of the Hongan Temple in Ise-Nagashima that ran from 1570 to 1574), Naomoto was killed in action while serving in the rear guard during the withdrawal of forces commanded by Shibata Katsuie.  Naomasa then succeeded Naomoto as the head of the clan.

Naomasa fought in numerous battles for Nobunaga.  In 1573, during the Siege of Ichijōdani Castle in Echizen Province, Naomasa succeeded in killing his former lord, Saitō Tatsuoki.  In 1579, when Araki Murashige attacked Inaba Sadamichi, Naomasa and Horikawa Kunimitsu repelled them.  Thereafter, he served meritoriously during the Ishiyama War against the followers of the Hongan Temple and during the subjugation of Murashige in a rebellion known as the Siege of Arioka Castle.

In the sixth month of 1582, Oda Nobunaga died unexpectedly in a coup d’état led by one of his senior retainers, Akechi Mitsuhide, in an event known as the Honnō Temple Incident.  Naomasa then cultivated friendly relations with Hashiba Hideyoshi (later known as Toyotomi Hideyoshi).  On 4/20 of Tenshō 11 (1583), after Hideyoshi deployed, although Horio Yoshiharu remained in Ōgaki Castle, he convinced Naomasa to join him in following Hideyoshi and deploy at Shizugatake.  Yoshiharu served an important role by providing security for Hideyoshi’s main division from the rear and encouraging Naomasa to deploy to Shizugatake proved a significant contribution to the ensuing conflict known as the Battle of Shizugatake.  Exchanges between Yoshiharu and Naomasa in this regard are recorded in historical accounts.

In 1583, Naomasa died and was succeeded by his younger brother, Ujiie Yukihiro.