His mother suffered from mental illness and he found refuge from the tumult of his family life in prayer and meditation at Christ Episcopal Church in Bordentown.

After graduating from Trinity in 1970, he enrolled at the General Theological Seminary of the Episcopal Church (M.Div., DD honoris causa) in New York.

Duncan served on the program committee of the Network for Anglicans in Mission and Evangelism, an agency created at the 1998 Lambeth Conference.

"[5][6] At the March 17, 2005, meeting of Episcopal Church's House of Bishops, Duncan read a speech in which he admitted that the rift between the two sides may be "irreconcilable".

[7] In a possible sign of schism, St. Brendan's, a liberal parish in Franklin Park, Pennsylvania, announced in February 2005 that it no longer wished to be under Duncan's oversight.

"[11] At the request of Rowan Williams, Duncan attended the 2007 Primates' Meeting in Dar es Salaam, Tanzania.

[12] Pending completion of this process, the three most senior bishops in the Episcopal Church had the option to inhibit Duncan from ministry but chose not to.

In her letter to Duncan, the Presiding Bishop stated that she "would welcome a statement by you within the next two months providing evidence that you once more consider yourself fully subject to the doctrine, discipline and worship of this Church.

On September 18, 2008, the House of Bishops voted that Duncan be deposed from ordained ministry on charges of "abandoning the communion of the Episcopal Church".

In the sentence Jefferts Schori declared that "from and after 12:01 a.m., Saturday, 20 September 2008, Bishop Duncan shall be deprived of the right to exercise the gifts and spiritual authority of God's word and sacraments conferred at ordination in this Church and further declare[s] that all ecclesiastical and related secular offices held by Bishop Duncan shall be terminated and vacated at that time.

Duncan stated that his role as archbishop was to "reunite a significant portion of our Anglican Church family here in North America" and indicated that he intended to serve for five years before stepping down.

[17] In October 2009, Duncan reacted to the Roman Catholic Church's proposed creation of personal ordinariates for disaffected traditionalist Anglicans by saying that although he felt that this provision would probably not be utilized by the great majority of ACNA's affiliated laity and clergy, he would happily bless those who were drawn to participate in this historic offer.

"[19] Duncan was one of the signatories of the statement of the Christian Associates of Southwest Pennsylvania, an organization representing 26 denominations, on April 13, 2012, expressly supporting the Roman Catholic Church in its opposition to the HHS mandate that would force Roman Catholic hospitals in the United States to pay for birth control methods not in accordance with the doctrine of the church.