Tadahisa was a son of the Shōgun Minamoto no Yoritomo (1147–1199) by the sister of Hiki Yoshikazu.
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 position of jitō (land steward) of the Shimazu Estate by Minamoto no Yoritomo, he took the name of Shimazu.
He sent Honda Sadachika to take possession of the province in his name and accompanied Yoritomo in his expedition to Mutsu in 1189.
His descendants ran the Shimazu clan (named after him) for hundreds of years.