During the patriarchal tenure of his cousin Antonije I (1571–1574), Gerasim became Metropolitan of Herzegovina.
In that time, his other cousin Mehmed Sokolović, from the Islamized branch of the family, held the post of the Grand Vizier of the Ottoman Empire (1565–1579) and acted as protector of the Serbian Patriarchate.
[2] As patriarch, Gerasim appointed his cousin Savatije Sokolović to be the next Metropolitan of Herzegovina.
In time, some disputes arose between two cousins, resulting in rivalry for the patriarchal throne.
Eventually, Metropolitan Savatije managed to succeed Patriarch Gerasim, probably in 1585 or 1586.