Benwell was born at Blenheim Palace in Oxfordshire where his father was under-steward to George Spencer, 4th Duke of Marlborough. He was a pupil of an obscure portrait painter called Sanders, who lived in Great Russell Street in Bloomsbury, London, but also studied at the Royal Academy Schools, where he was awarded a silver medal in 1782. He later taught drawing at Bath, and executed a few small oval drawings in a technique which combined watercolour and pastel. His works have suffered much from the ravages of time.[1]
He returned to London[1] and exhibited a classical subject, Glycaera at the Tomb of her Mother,[2] at the Royal Academy in 1784, but died of tuberculosis the next year, and was buried in Old St. Pancras churchyard.[1]
Several of his works became well known from engravings. They included two scenes from "Auld Robin Gray"; the "Children in the Wood", engraved by William Sharp; and A St. Giles's Beauty and A St. James's Beauty, both engraved by Bartolozzi.[1]
