[2] He studied for the priesthood at St Patrick's College, Maynooth, and was ordained a priest of the Diocese of Clogher in 1937, a classmate of Cardinal William Conway.
He became the first President of St Michael's College, Enniskillen in 1957, retiring from that position in the summer of 1966.
[3] Mulligan's appointment as Bishop of Clogher was made on 28 November 1969 and he received episcopal ordination two months later on 18 January 1970.
The Archbishop of Dublin John Charles McQuaid was invited to concelebrate the ordination Mass but refused to participate in this then novel way.
[citation needed] Mulligan died on 21 January 1990, aged 77 years and is buried in the grounds of his Cathedral, alongside his predecessor.