Also known as Xanthopoulos, Isidore suceeded in the Ecumenical throne Gennadios after his resignation in May 1456. Her remained a Patriarch until his death on the 31st March 1462. Athanasius Konmenos Ypsilantis mentions the following:
After the resignation of Mr Gennadios, the hieromonk and spiritual father Isidore, from the Xanthopoulos family, ascended onto the Ecumenical throne, by vote and test of a local council, after having been chosen a common and loved father of all the civilians, and ordained a Bishop in the temple of the Pammakaristos by the Metropolitan of Heraklia and the other concelebrating bishops, and gived by the Sultan Mechmet the usual gifts, he received the same acceptance as his predecessor.
We do not have any information about his work except for one decision regarding the orthodox of Venice, but the fact that he remained a Patriarch for six years implies, as T.Gritospoulos notes, that in spite of the tempest the humble Patriarch fulfilled his duty and kept the office, hard though it was for him to succeed a man such as Gennadios the Scholar.