Knowles died, unmarried, at Ashburton, Devonshire, on 21 July 1841, aged 60. He was one of the original members of the Athenæum Club, and his portrait, drawn by Charles Landseer, is No. 25 of the series of lithographs, published as Athenæum Portraits, by Thomas McLean. He was corresponding member of the Philosophical Society of Rotterdam.
