The possibility of Edmonstone, a barrister on the home circuit, entering Parliament like his father for Dunbartonshire, was mentioned in 1801, when it was considered as a bait for his father’s giving his interest in Stirlingshire to his friend and kinsman the Duke of Argyll for the benefit of the ministerial candidate.
Edmonstone commenced his canvass for Stirlingshire in March 1811, backed by the Duke of Montrose and Lord Melville: his only handicap was his being little known, which he was urged to remedy. He was so strongly supported that the sitting Member Charles Elphinstone Fleeming declined a poll in 1812. Edmonstone went on, as expected, to give a silent support to ministers. His only known wayward vote was on 17 June 1816, on the Irish vice-treasurer’s salary. He voted against Catholic relief on 11 and 24 May 1813, 21 May 1816 and 9 May 1817. He opposed inquiry into popular education, 3 June 1818. In April 1818, threatened with a contest, he denied the rumour that he was withdrawing and easily defeated his opponent. On 18 May 1819 he voted with government against Tierney’s censure motion and on 10 June for the foreign enlistment bill. Early in the spring of 1820 he was seized with paralysis.
