Isidore was an ethnic Greek born in Thessaloniki during the latter part of the 1290s where he became a teacher and spiritual guide.
In 1344, Isidore, who was at the time the bishop elect of Monemvasia, and Gregory Palamas were excommunicated by a synod of anti-hesychast bishops that had been convened by Patriarch John XIV of Constantinople who himself was an opponent of Saint Gregory.
Upon becoming patriarch, Isidore I released Gregory Palamas from prison and consecrated him Metropolis of Thessaloniki.
During the two and a half years of his patriarchate, Isidore I sought to have the whole Byzantine Church accept the Palamite dogmas.
[2] Evangelos C. Pringipakis, "Patriarch Isidore I Boucheiras (± 1290–1350) in the Writtings of Demetrius Cydones", Byzantinos Domos 29 (2021), s. 417–439.