Greek Orthodox lay theologian and liturgist who eminently represents the tradition of Byzantine theology. He wrote extensively on Hesychast mysticism (a traditional method of Byzantine Christian contemplative prayer that integrates vocal and bodily exercises) and on the theology of Christian life and worship.

In the Byzantine civil war between the rival emperors John V Palaeologus (1341–91) and John VI Cantacuzenus (1347–54), Cabasilas sided with Cantacuzenus' more conservative policies, performing several diplomatic missions and supporting the positions of the theologian Gregory Palamas (1296–1359). Cabasilas' work Commentary on the Divine Liturgy is one of the foremost explanations of Christian sacramental worship that exist.

Cabasilas' chief spiritual–ascetical writing, Life in Christ, proposed a program of Christian spirituality integrating divine and human activity in both individual and common liturgical prayer. By essays and political involvement he manifested a social consciousness relative to economic and institutional (including the church) inequities. The high intellectual level of his conferences and sermons and the sensitivity of his religious poetry have gained an international audience.