Born in 1205, son of second regent Hojo Yoshitoki; his mother is believed to have been from the Iga clan. He grew up close to the shogunate's inner circle and served in key offices including the hyojoshu and as rensho (co-regent). After fifth regent Tokiyori took Buddhist vows in 1256 and nominally passed the regency to Nagatoki, Masamura continued supporting governance as a seasoned elder statesman. When the sixth regent Nagatoki died of illness at 35 in 1264, Masamura became the seventh regent. By this time the shogunate was facing unprecedented diplomatic pressure: the Mongol Empire's first diplomatic letter demanding submission arrived in 1268. Masamura used his long experience to keep the shogunate stable while preparing a smooth transition to his son Hojo Tokimune as the eighth regent. In 1268, once Tokimune assumed the regency at age 18, Masamura stepped aside and continued to support the shogunate as a senior elder. He died in 1273 at 69. He was a quiet guardian of continuity in a time of gathering storm.

Gentle and stable in his governance. In turbulent times he worked to maintain order within the shogunate.

He stabilized the shogunate on the eve of the Mongol invasions and achieved a smooth transfer of power to Tokimune. As an elder statesman he contributed to the shogunate's stability.