When his elder brother MINAMOTO no Yoritomo rose up in arms in Izu Province on August 17, 1180 (old old lunar calendar) to defeat the Taira clan (Jisho-Juei War), he rallied to joined the banner of his brother.
治承4年（1180年）8月17日_(旧暦)に兄源頼朝が伊豆国で挙兵すると、その幕下に入ることを望んだ義経は、兄のもとに馳せ参じた。