the rest of donkin's life passed in literary and political work. he was one of the original fellows of the royal geographical society, and was a member of the royal society and of many other learned bodies. his theories as to the course of the river niger, published under the title "dissertation on the course and probable termination of the niger" (london, 1829), involved him in a good deal of controversy. from 1832 to 1837 he sat in the house of commons as member of parliament (mp) for berwick-upon-tweed, and in 1835 became surveyor-general of the ordnance. he was elected as mp for sandwich in 1839, and held that seat until he committed suicide at southampton on 1 may 1841. he was then a general, and colonel of the 11th regiment of foot.