Ardagh is derived from the Irish Ardacadh, or Ardach which means 'high plain' or 'high field'. Carrickerry is derived from the Irish Carraig Chiarraí, which means 'the Rock of Ciarraí or Kerry'. The Ciarraí were a Celtic tribe who also gave their name to the county of Kerry.
Ardagh was an important centre in medieval times. It was once a manor belonging to the Bishop of Limerick. With the development of Newcastle West, Ardagh's importance began to decrease. In 1981 a large hilltop fort, covering 52 acres, was discovered in the townland of Ballylin, a mile north-west of Ardagh. It is the largest ring fort found in Ireland so far.
The parish was initially amalgamated with Newcastlewest, until their separation during the tenure of Fr William Hourigan PP sometime between 1755 and 1764. Carrickerry became a joint parish with Ardagh under the stewardship of Fr Michael Maher, which lasted from 1871 to 1881.