He was ordained in 1802, and engaged in clerical work at Turkdean, Gloucestershire, and Salisbury.
Between 1823 and 1828 Duke contributed to the Gentleman's Magazine, chiefly on Wiltshire antiquities.
In his Druidical Temples of the County of Wilts (1846), he maintained that the early inhabitants of Wiltshire had "pourtrayed a vast planetarium or stationary orrery on the face of the Wiltshire downs", the earth being represented by Silbury Hill, and the sun and planets, revolving round it, by seven "temples", four of stone and three of earth, placed at their proper distances.
[1] A review in the Christian Remembrancer said "it has seldom been our unhappy fate to wade through a book, in the pages of which we could find less instruction of any kind, or a larger number of the most puerile absurdities".
The eldest son, Edward, entered the church and succeeded to the estates.