According to a record of his life, he was reportedly born in Sumiyoshi Taisha in Osaka. He was initially Koremune no Tadahisa (惟宗忠久) but after being given the territory of Shimazu, Hyūga Province to rule from by Minamoto no Yoritomo, he took the name of Shimazu.
He received the domain of Shioda (Shinano province) in 1186 and was then named Shugo of Satsuma province. He sent Honda Sadachika to take possession of the province in his name and accompanied Yoritomo in his expedition to Mutsu in 1189. He went to Satsuma in 1196, subdued Hyūga and Ōsumi provinces, and built a castle in the domain of Shimazu (Hyūga) which name he also adopted. He is buried in Kamakura, near his father's tomb.