Minamoto Chikamoto was born in 1176 to Kamakura Minamoto daimyo Minamoto Yoritomo and his wife Minamoto Masako, their first child. He held the title of heir since his birth, and was used as a valuable hostage. When the Minamoto allied with the Ishikawa, he was sent to them and put under their protection in exchange. Later, he was sent to the Kikuchi, and after a brief stay, was returned home.
Chikamoto came of age at fourteen, and was made a general during the Kenkyu War, which occurred during the time of his coming of age. His father Yoritomo died fighting the Hiraizumi Fujiwara while he was 15 and Chikamoto became the new daimyo. He adopted Sasaki Shigekiyo as his heir in order to secure a successor, as his adoptive brother Minamoto Mitsunao was disloyal and also his brother; only a son could succeed him.