In 1283, Gregory was chosen Patriarch of Constantinople. Occupying the patriarchal [[see]], he inherited the political and religious problems that had grown through the Latin occupation and the unionist [[Council of Lyon]] of 1274. The issues that arose from the aggressive attempts for union with Rome by Emperor Michael VIII and Patr. John XI Beccus became entangled with the controversy over the ‘’filioque’‘.
In the Spring of 1285, Gregory called the Synod of Blachernae to resolve the dispute between the followers of [[Arsenius Autoreianus of Constantinople|Arsenius]] and [[Joseph II of Constantinople|Josephus II]] concerning their unionists positions and the filioque. During the synod, Gregory presented his position on the filioque in his Tome<ref>http://www.geocities.com/trvalentine/orthodox/tomos1285.html - Exposition of the ''Tomus'' of Faith Against Beccus</ref> opposing John XI’s theological innovation. In his Tome, Gregory presented not just a repeat of the formulations of Photius and Athanasius, but a reasoned theological contribution that worked out the implications of writings of the [[Cappadocian Fathers]] and [[John of Damascus]] on the procession of the [[Holy Spirit]].
Patr. Gregory’s contemporaries did not see the impact of his insightful words. These words became the forerunner of fourteenth century Palamite Theology. While his contemporaries generally accepted his orthodoxy, they pressured him to resign, which he did in 1289. That he did resign and not continue to press the issue is evidence of his pastoral sensitivity to the importance of healing of the political divisions that were tearing the church during his lifetime.