He will replace Sadeq Amoli Larijani who resigned from his post earlier.
In a decree on Saturday, the Leader thanked Amoli Larijani for his services and named Hosseini Khorasani as a new member of the council.
The Guardian Council is a constitutionally mandated 12-member council in Iran that, among other things, is tasked with ensuring the compatibility of the legislation passed by the parliament with the criteria of Islam and the Constitution.
Six of its members – religious scholars - are appointed by the Leader of the Islamic Revolution and the other six – law experts, are named by the Judiciary chief.
Those nominated by the Judiciary chief should be endorsed by the Parliament.