Because Yoshitane ASHIKAGA, who had opposed his father and reassumed the shogunship, had been driven out from Kyoto as a result of his confrontation with Takakuni HOSOKAWA, the kanrei (shogunal deputy), in 1521, Yoshiharu was supported by Takakuni to become the twelfth shogun.
大永元年（1521年）、父と対立して将軍職に再任していた足利義稙が、管領の細川高国と対立して京都から追放されたため、高国に擁立されて第12代将軍に就任した。