His episcopal consecration took place at St Eunan's Cathedral in Letterkenny on 28 March 1982, the principal consecrator was Cardinal Tomás Ó Fiaich, and the principal co-consecrators were Gaetano Alibrandi, titular Archbishop of Binda, and Edward Daly, Bishop of Derry.
[2] A brusque man with an abrupt air about him and small of stature, he was described by one Maynooth College professor as a "cross between Mussolini and the Child of Prague."
[2] In November 2009, Bishop Hegarty expressed concern after 17 priests in the Derry diocese were found to have child sexual abuse allegations filed against them.
[5] In 2010 the Belfast Telegraph and other media outlets reported that Bishop Hegarty was a named defendant in a civil legal action concerning the alleged abuse of a young girl by a priest of the Derry diocese.
On 7 November 2011, he issued a statement saying that, having been diagnosed with "a condition which is, unfortunately, irreversible and progressive", he had submitted his resignation because he was no longer able to fulfill his role as diocesan bishop.