Before emigrating to Australia in 1837 Duncan had established himself in Aberdeen as a bookseller, journalist, teacher and publisher. In New South Wales, he worked initially as a teacher in Maitland before founding the Australasian Chronicle(1839) and the Weekly Register (1843). As noted by the Australian Dictionary of Biography, the literary columns of the Register revealed Duncan as 'an intelligent critic and the patron, publisher and friend of colonial poets', especially Charles Harpur and Henry Parkes (qq.v.). After the Register's demise in 1845, Duncan worked in the Customs Service, in Moreton Bay (1846-1859) and Sydney (1859-1881).
Duncan published works by both Henry Parkes and Charles Harpur in his Register, as well as Harpur's Thoughts, A Series of Sonnets (1845). His own writing included pamplets on a wide range of political and social topics.