Born in 1129 into the Yamakage branch of the Fujiwara Hokke, Tomomune settled in 1156 in the Nakamura estate of Haga District, Shimotsuke Province (present-day Moka City, Tochigi), where he built a residence southeast of Nakamura Hachimangu Shrine and took the name "Nakamura Taro." He joined Minamoto no Yoritomo's uprising in 1180, and in the 1189 Oshu Campaign his four sons led the vanguard, capturing the Ishinazaka fortress in Shinobu District — the front-line base of Fujiwara no Yasuhira's forces — and taking its commander Sato Motoharu prisoner. For this achievement, Tomomune was granted Date District in Mutsu Province, including the fiercely contested Atsukashiyama battleground, as a jito (land steward), and adopted the surname "Date." His second son, Munemura (Tameshige), inherited Date District and became the progenitor of the illustrious Date clan of Oshu, while his third son, Suketsuna, inherited Nakamura in Shimotsuke and continued the direct line of the Shimotsuke Nakamura clan. Tomomune died in 1199 at age 71.

A decisive, capable commander who committed his entire family to Yoritomo's cause and led his sons to victory in the fierce fighting of the Oshu Campaign.

By taking the Date surname after his exploits in the Oshu Campaign, he laid the foundation of the illustrious Date clan of Oshu, which would later produce Date Masamune. Nakamura Castle, his original base, passed to the Shimotsuke Nakamura clan and survives today as a prefectural historic site.