Sanesuke's grandfather, Saneyori, was the eldest son of FUJIWARA no Tadahira, who served as Sadaijin (Minister of the Left) during Emperor Murakami's reign, as Kanpaku (Chief Adviser to the Emperor) during Emperor Reizei's reign, and as Sessho (Regent) during Emperor Enyu's reign.
祖父の実頼は摂政関白を歴任した藤原忠平の長男で、村上天皇のときに左大臣、冷泉天皇のときに関白、円融天皇のときに摂政を歴任した。