Saint Nissen was an early Christian convert who was abbot of a monastery in County Wexford, Ireland.
Life
Saint Nissen was converted to Christianity by Saint Patrick. He became abbot of Montgarth (Mountgarret) Abbey in Wexford, Ireland.
His feast day is 25 July.[1]
NISSEN (St.) Abbot (July 25) (5th cent.) A convert in Ireland made by Saint Patrick, who set him over a monastery at Montgarth (Mountgarret) in the present county of Wexford.[2]
Butler's account
The hagiographer Alban Butler ( 1710–1773) wrote in his Lives of the Primitive Fathers, Martyrs, and Other Principal Saints, under April 9,
Saint Nissen, Abbot
Whom Saint Patrick baptized, ordained deacon, and appointed abbot of Montgairt or Mountgarret, in the county of Wexford, on the borders of Kilkenny, of which place he is titular saint. See Colgan in MSS. ad 25 Julij.[3]