Haga Takasada served as a bushō during the Sengoku and Azuchi-Momoyama periods.  He was a retainer of the Utsunomiya clan of Shimotsuke Province.

In 1521, Takasada was born as the third son of Mashiko Katsumune, a retainer of the Utsunomiya clan.

In 1541, Haga Takatsune rebelled against the Utsunomiya and was killed by Utsunomiya Hisatsuna.  Thereafter, upon orders of Hisatsuna, Takasada inherited the Haga clan.

In 1549, after Hisatsuna died fighting against Nasu Takasuke at the Battle of Kitsuregawa-Sōtomezaka, a powerful retainer named Mibu Tsunafusa took over Utsunomiya Castle, whereupon Takasada took Hisasada’s young son named Ise Jumaru (later known as Utsunomiya Hirotsuna) and fled to the base of the Haga clan at Mooka Castle.  Takasada then served as a deputy to Hirotsuna with the aim of revitalizing the clan.  In 1551, Takasada launched a plot to have Senbon Suketoshi, the lord of Senbon Castle in the Haga District, lure and kill Takasuke at the castle as a means to gain retribution for the killing of Hisatsuna in battle.  In 1555, he compelled Haga Takateru (Takatsune’s son) to take his own life following ongoing resistance toward the Utsunomiya clan.

In 1556, Takasada demanded Satake Yoshiaki of Hitachi Province (via Edo Tadamichi (whose mother originated from the Haga clan), Ashikaga Yoshiuji (the Koga kubō), and Hōjō Ujiyasu (whose authority reached across the Kantō)) to recapture Utsunomiya Castle, whereupon the Satake army marched to Tobiyama Castle, ousted Mibu Tsunatake from Utsunomiya Castle, and, in name and in substance, enabled Hirotsuna to return to the Utsunomiya clan.

Thereafter, he entered into a political relationship through marriage with the Satake clan, and, further, forged ties with the Gohōjō, transferred headship of the clan to Haga Takatsugu (the younger brother of Takateru who was harbored by Mashiko Iemune), and then lived in seclusion.