Dermot went to University College Dublin, where he studied English and Philosopy. In 1974 he took up a teaching post, but left 2 years later to persue the comedy career that he had started at university.

In 1979 his first introduction to TV came with an appearance on "Live Mike" on RTE television as Fr. Trendy, a catholic priest who was religiously hip. He became a regular for the next 4 years.