By sixteen, he was assigned prefect (bugyō) in charge of the construction of shōgun Ashikaga Yoshiaki's residence at Hongaku-ji, working with the likes of Sugaya Nagayori, Ōtsu Nagaaki, Yabe Iesada, Hasegawa Hidekazu, Manmi Shigemoto and Fukutomi Hidekatsu.

In 1581, Hidemasa fought in Second Tenshō Iga War and followed Oda Nobutada into battle against the Takeda clan at Siege of Takatō (1582) and was granted the fief of Sakata Domain, in Ōmi Province, with an income of 25,000 koku.

Hidemasa was promoted to the fifth rank, appointed to the Saemonfu (左衛門, Court Security Office), and granted Sawayama in Ōmi Province as his fief, with an income of 90,000 koku.

Hidemasa led portions of Hideyoshi's forces once again, in the 1584 Battle of Komaki and Nagakute, in which they suffered a crushing defeat at the hands of the Tokugawa army.

The following year, Hideyoshi became Kampaku (Imperial regent), and Hidemasa was promoted to the fourth rank at court, and appointed to a new post as well.

Following the siege of Negoro-ji and the invasion of Shikoku (1585), he was given the lands of the late Niwa Nagahide, Kita no shō in Echizen Province, with an income of 180,000 koku.