Duncan was born in Clyde, New Zealand, and graduated from the University of Otago. As an educator he rose to the position of inspector of schools for the New Zealand Education Department and made a significant contribution to the introduction of the new mathematics curriculum. He wrote text books that were extensively used in New Zealand primary schools and which were also published in the United States. In 1958 he moved to the North America as a university lecturer and he received his doctorate from Columbia University.
In 1961, Duncan became headmaster of Newington College, an inner-city Sydney private boys school. He immediately proposed that the school should be moved to a larger site in the northern suburbs but this suggestion met with resistance from the college council. Before the end of the academic year he had resigned and returned to the United States.
In 1962, Duncan became professor of mathematics at Rutgers University and at the time of his retirement, in 1977, was chairman of the department of curriculum and instruction in the Graduate School of Education. In 1982 he set aside a Trust fund to endow annual awards for "excellent teachers of Mathematics" in New Zealand and the United States. He died in a Morristown, New Jersey hospital of leukemia on November 25, 1990. He lived in Bernardsville, New Jersey and was survived by his wife, Lois, two daughters and a son.
- "Dr. Ernest Duncan, 74, Mathematics Professor", The New York Times, November 28, 1990. Accessed March 21, 2011. "Dr. Ernest R. Duncan, professor emeritus of mathematics at Rutgers University and the author of several mathematics textbooks, died on Sunday at Morristown Memorial Hospital in New Jersey. He was 74 years old and lived in Bernardsville, N.J. He died of leukemia, his family said."
- Modern School Mathematics, published by Houghton Mifflin
- D. S. Macmillan, Newington College 1863–1963 (Syd, 1963)
- P. L. Swain, Newington Across the Years 1863–1998 (Syd, 1999)
- A. H. McLintock, Encyclopaedia of New Zealand, 'Expatriates – Biographies' (N.Z., 1966)
Rev Douglas Trathen