He founded an early Christian monastery of Athleague, in county Roscommon.

Moran provides the following local perspective:- The sanctity of Manchán of Athleague is first recorded in the Annals of the Four Masters which records "A.D. 1493, .. Irish: Ath Liacc Maenaccáin (Middle English: Ath liag-Maenagain)",[3] which confirms he was patron saint of Athleague, in County Roscommon.

The "Martyrology of Donegal" records the Saint as "Latin: Maonacan Atha liacc, 7 Feb., Maonacan, of Ath-liacc",[4] while "The martyrology of Gorman" notes "Moenucan, of Ath liacc, Feb. 7.

[5] The multiplicity of Saints called Maenucan, Maonacan, Moenagain Irish: Manchán, Manachán, Mainchéin, Mainchin, Monahan Latin: Manchianus, Manichchaeus is because the name is a diminutive of Irish: Manach Latin: Monachus, a monk,[6] so the real names of each recorded Saint Manchan are unknown.

[1] The Annals of the Four Masters calls Athleague the medieval names of- "Middle English: Athliag Maenagan, and Irish: Atha Liacc Maonaccan".