Saint Nissen was an early Christian convert who was abbot of a monastery in County Wexford, Ireland.
He became abbot of Montgarth (Mountgarret) Abbey in Wexford, Ireland.
[1] The monks of St Augustine's Abbey, Ramsgate, wrote in their Book of Saints (1921), 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.
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.