Duncan was born on June 12, 1826 in Bathurst Township. He was baptised on the 28th of June in a Presbyterian church in Perth, Ontario. In 1852 he married Mary A. Burke in Christ Church, Oso township.

Duncan died at the Kingston General Hospital on September 27, 1901 at the age of 75 from cancer of the face. Mary died in Oso township from pneumonia on January 19, 1927 at the age of 96. Both are buried at Christ Church Anglican in Oso township. Duncan and Mary had eight sons and four daughters.