Born in Beirut, Derderian studied at the Antelias Seminary and the Seminary of the Holy See in Etchmiadzin, Armenia. Upon his graduation in 1980 he was ordained a celibate priest by Vazken I, Catholicos of All Armenians.
Following his ordination, Derderian attended St Stephen's House, Oxford in England, where in 1983 he obtained his bachelor's degree in theology. After a year lecturing at the seminary in Etchmiadzin, Derderien was appointed pastor of the Holy Trinity Armenian Church in Toronto, Ontario, Canada, where he served for six years. In appreciation for his services he was honoured with an encyclical by Vazken I in 1986.
In 1987 Derderien received his master's degree in theology from Oxford University and was raised to the rank of Dzairakuyn Vartabed. In 1990 he was elected primate of the diocese of the Armenian Church in Canada and, later the same year, was ordained as a bishop by Vazken I in the Cathedral of St. Etchmiadzin. On 18 February 1993 he was made an archbishop and was re-elected as Primate of Canada in 1995 and again in 2000. During his tenure in Canada, he initiated many missions in support of the newly independent Armenia, including the Canadian Youth Mission to Armenia (CYMA), which he founded in 1992 in cooperation with a group of young volunteers within the community led by university student Ronald Alepian.
On 3 May 2003, Derderian was elected Primate of the Western Diocese of the Armenian Church of North America by the 76th Annual Assembly.