He was born as the ninth son of MINAMOTO no Yoshitomo, the head of the Kawachi-Genji (Minamoto clan), which is a family descended from the Seiwa-Genji (Minamoto clan) and was called Ushiwakamaru.
清和源氏の流れを汲む河内源氏の当主源義朝の九男として生まれ、牛若丸（うしわかまる）と名付けられる。