Laisrén (Mo-Laisse) (d. 639/41), bishop of Lethglenn (Leighlin, Co. Carlow), and saint in the Irish tradition, was according to his genealogy son of Cairell, who belonged to the Dál nImde, a population group located among the Ulaid (Ulstermen). A tract on the mothers of the Irish saints names his mother as Maithgemm, daughter of Áedán (qv) son of Gabrán, king of Dál Riata. Tradition relates that he was brought up in Scotland. After completing his basic education he travelled to Rome, where he spent four years and was ordained priest by Pope Gregory I. He returned home to Ireland with copies of biblical manuscripts and entered the monastery of Gobbán (qv) at Lethglenn.
Gobbán later resigned his abbacy to which he appointed Laisrén. Under Laisrén's rule Lethglenn became a major monastery; it is reputed to have numbered 1,500 monks at the peak of its success. Laisrén played an important role in winning over the southern Irish churches to the Roman Easter dating. He attended the synods of Mag Léne (630) and Mag nAilbe (631), where he encountered the opposition of Fintan (qv) (d. 637) to the new Easter dating. He is said to have gone with others on a delegation to Pope Honorius (625–38) sometime after 632 to receive a definitive settlement of the Easter question. This, his second visit to Rome, is mentioned in the ‘Codex Salmanticensis’ of Irish saints’ Lives. Laisrén is included in the Irish litany of pilgrim saints, and is commemorated in all the Irish martyrologies on 18 April. His name is also attested in many Scottish place-names.