With his relative, King Guaire Aidne mac Colmáin (d. 663) of Connacht he founded the monastery of Kilmacduagh, ("the church of the son of Duac"), and governed it as abbot-bishop.

St Colman was reportedly the son of Queen Rhinagh and her husband the chieftain Duac, born in Kiltartan, now County Galway.

[1] He was educated at Saint Enda's monastery on Inishmore/Árainn, the largest of the Aran Islands[2] and lived there as a hermit.

[5]: 58–9 King Guaire Aidne mac Colmáin had his principal place of residence at Kinvara, near the location of today's Dunguaire Castle.

Upon learning of the hermitage, he was so impressed with Colman's holiness that he asked him to take episcopal charge of the territory of the Aidhne.

[3] In 610, Colman founded a monastery, which became the centre of the tribal Diocese of Aidhne, practically coextensive with the See of Kilmacduagh.

[1] Although the "Martyrology of Donegal" assigns his feast to 2 February, yet the weight of evidence and the tradition of the diocese point to 29 October.

[5]: 59 While she carried the child in her womb, Colman's mother heard a prophecy that her son would be great man and surpass all others of his lineage.

However, the king's men caught up to her and tried to drown her in the Kiltartin river by tying a stone around her neck.

Not long after she gave birth to Colman (c. 560), Rhinagh took her newborn to a priest to baptise, but they realised there was no water.

[5]: 58 It is said that Colman declared that no person nor animal in the diocese of Kilmacduagh would ever die of lightning strike, something that appears true to this day.

Although it was in the custodianship of the O'Heynes of Kiltartan (descendants of King Guaire) and their relatives, the O'Shaughnessys, it can now be seen in the National Museum in Dublin (Attwater, Benedictines, Carty, D'Arcy, Farmer, MacLysaght, Montague, Stokes).

But the monks wanted to pray during the night hours, too, and couldn't count on the rooster to awaken them at midnight and 3:00 am.

When he did not awake at the usual hour in the middle of the night for Lauds, the mouse pattered over to the bed, climbed on the pillow, and rubbed his tiny head against Colman's ear.

When he regained his composure, Colman praised the clever mouse for his faithfulness and fed him extra treats.

Each day, Colman would spend some time reading a large, awkward parchment manuscript prayer book.