This author was the youngest son of John Duncombe, Esq. of Stocks, Hertfordshire. He was privately educated, and in early life obtained a clerkship in the navy office. His first acknowledged production was a translation of the 29th ode of the first book of Horace. In 1721 he published a translation of the Carmen Seculare.
In 1732 he appeared as a dramatic author. His tragedy of Lucius Junius Brutus was brought out at Drury-lane, in the winter of that year, with moderate success. In 1759, with the aid of his son, he completed a translation of Horace, with notes and other apparatus. Besides these works Mr. Duncombe wrote a number of miscellaneous pieces, and edited the remains of his brother-in-law, Jabez Hughes, and of Mr. Samuel Say, a dissenting minister. He died in 1766.