WM missionary in Jamaica, born in Dundee. He was appointed to Jamaica in 1821, where the struggle for the emancipation of slaves was still being fought out in the wake of the abolition of the slave trade in 1807. In 1823 , under pressure from abolitionists, many of them Methodists, Lord Bathurst produced his 'Amelioration Proposals', designed to improve the lot of the slaves. They raised the expectations of the slaves, but were largely ignored by the planters and led to slave riots, for which the missionaries were widely blamed, suffering threats and physical violence. They, in a letter to the colonial governor, sought a middle way which fell short of condemning slavery as an institution, and for this they were condemned by the Missionary Committee in London. Following a serious slave insurrection in 1831, Duncan returned home in 1832 with his health impaired and was called to give detailed evidence from his first-hand experience to the parliamentary committee on the emancipation of slaves, answering 487 questions in five days.
In 1841 he became Superintendent of the Edinburgh Circuit and the following year Chairman of the newly-amalgamated and poverty-stricken Edinburgh and Aberdeen District. His novel suggestion that Scots received into the ministry should be required to stay in Scottish circuits and, because living was cheaper than in England, be paid less than their English colleagues, was a predictable non-starter. He died on 21 January 1862.
'His testimony [on West Indian slavery] told powerfully on the heads and hearts of his examiners, and hastened the delivery of the Negro. Would have made an excellent barrister.- Shrewd, -wary,- foreseeing, like most Scotchmen… A good preacher;- powerful, convincing, impressive… A pleasing, though not a harmonious voice.- A cheerful and instructive companion.'
Wesleyan Takings (1840), pp.361-2