He represented Wigtown Burghs from 1874-1880 and again for a few months later in 1880 and also sat for Kirkcudbrightshire between 1885 and 1906 and briefly in 1910. In 1880 he assumed the additional surname of MacTaggart. On 7 October 1892, he was made a Baronet, of Southwick in the Stewartry of Kirkcudbright and Blairderry in the County of Wigtown.
MacTaggart-Stewart died in September 1923, aged 88.
He was succeeded in the Baronetcy by his only surviving son, Sir Edward Orde MacTaggart-Stewart, 2nd Baronet.