Comgall was educated by St. Finnian of Clonard and by St. Mobhi of Glasnevin among the Twelve Apostles of Ireland — the great generation of Irish monastic founders. Around 558 he founded the monastery of Bangor on the northern shore of Belfast Lough.
Bangor under Comgall's rule became one of the principal centers of Irish Christianity, famous across Europe for the rigor of its observance and the quality of its scholarship. The Antiphonary of Bangor — a 7th-century liturgical manuscript now at the Ambrosian Library in Milan — preserves the unique liturgy of his foundation. The community at its height numbered three thousand monks.
Among his disciples were St. Columbanus (whom he formed for the European mission), St. Gall (founder of St-Gallen in Switzerland), and many of the great Irish missionaries who took the Christianity of the Celtic north to the continent. Through Comgall's school the Irish monastic tradition reshaped Carolingian and post-Carolingian Europe.