Gregorios 45 was hegoumenos of the monastery of Hormisdas; in 787 he attended the Second Council of Nikaia (the Seventh Ecumenical Council); he is attested at the fourth session, on 1 October 787, when he produced a codex containing works by Sophronios of Jerusalem: Mansi XIII 57 (Γρηγόριος ὁ εὐλαβέστατος μοναχὸς καὶ ἡγούμενος μονῆς τῶν Ὁρμίσδου). Later at this session he subscribed the statements read out from the Fathers in support of the veneration of icons: Mansi XIII 152 (Γρηγόριος ἡγούμενος τῶν Ὁρμίσδου). Since archimandrites, abbots (hegoumenoi) and monks attended all other sessions of the Council (see Mansi XII 999 (abbreviated), XII 1051, XII 1114, XIII 4, XIII 157, XIII 204, XIII 373 (abbreviated), where the texts read: παρόντων καὶ τῶν θεοφιλεστάτων ἀρχιμανδρίτων τε καὶ ἡγουμένων καὶ πάντος τοῦ μοναχικοῦ πληρώματος or similar), Gregorios 45 probably attended other sessions of the Council.

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