Bishop Dunn was educated at St Michael's School in Remuera, at Auckland's Sacred Heart College, and then at the University of Auckland.
Bishop Dunn studied for the Catholic priesthood under the Jesuits at Holy Name Seminary Christchurch from 1969 to 1970, and under the Vinebtians at Holy Cross College in Mosgiel from 1971 to 1976. He was ordained a priest at St Michael's Church in Remuera on the 24th of April 1976. He then carried out pastoral work with Maori in Mangere East and he lived at the Auckland Catholic marae, the Te Unga Waka Marae in Epsom. Later, he served in the Auckland suburbs of Takapuna, Pakuranga, and Northcote. In 1986 and 1987, he was Director of Vocations for the Diocese of Auckland. In 1992, he was appointed pastoral assistant to the Bishop of Auckland, Denis Browne.
On the 24th of July 1994, Dunn was ordained to the episcopate as an auxiliary Bishop of Auckland.
On the 24th of December 1994, Dunn was appointed Bishop of Auckland to succeed Browne who had been named Bishop of Hamilton and he [Dunn] was installed as Bishop of Auckland in St Patrick's Cathedral in Auckland on the 29th of March 1995.
AUCKLAND MARIST BROTHERS OLD BOYS RUGBY CLUB