Dundas was an amiable, unassuming young man, completely dominated by his ambitious father, who, having purchased control of Richmond, offered Lord Ancram £4,000 to vacate his seat in favour of Thomas.
In 1766 Sir Lawrence, shortly after purchasing the controlling interest in Orkney, proposed his son as candidate at the next election;
In 1774 Thomas was returned for Richmond, but having secured re-election for Stirlingshire relinquished Richmond to his cousin Charles. Both he and Charles had been indirectly involved in a controversy in the burgh of Stirling resulting in the exposure of a system of corruption which occasioned the town’s disfranchisement.
This probably marks the beginning of Dundas’s interest in parliamentary and burgh reform, despite his father’s notoriety in election affairs. In 1777 Sir Lawrence, violently attacked in Edinburgh by Henry Dundas and the Buccleuch interest, deputed Thomas to vindicate his conduct, and even the scurrilous pamphleteers found little to defame in ‘Tommy’s’ personal conduct.
In Parliament he supported Administration until 1779, when his father became disgusted with North’s mismanagement of the war. During the summer Thomas helped to raise a regiment, with Lord Fauconberg as colonel and himself as lieutenant-colonel.
Re-elected unopposed for Stirlingshire, on a compromise with Lord Graham, Thomas assisted and advised his father in Edinburgh and the other contested elections in which the family interest was engaged. In the new Parliament Sir Lawrence, while remaining hostile to North and Henry Dundas, sought to maintain his personal connexion with Sandwich, to whom Thomas wrote on 22 Sept. 1781, immediately after his father’s death:
After Rockingham’s death Sir Thomas adhered to Fox, and voted against Shelburne’s peace preliminaries, 18 Feb. 1783. He voted for Pitt’s parliamentary reform bill on 7 May 1783, and thereafter directed his main efforts to the internal reform of Scottish burghs.
In August 1783 he obtained from Portland the office of lord advocate for his boyhood friend Henry Erskine,
At the general election he secured Stirlingshire for himself, Orkney for his cousin Thomas, and Tain Burghs for Charles Fox. Patrick Graeme, the sheriff of Orkney, wrote to a friend:
I know Sir Thomas from being at College with him. I regard and esteem him and both his cousins as among the most gentlemanly and good-tempered people I ever knew ... he has it not in his nature a wish to oppress or injure any one.
Sir Thomas, in conformity with his liberal views, was ‘very well inclined’ to bring on to the electoral roll the hitherto unrepresented freeholders of Shetland, whatever their political attitude.
He voted for Pitt’s reform proposals, 18 Apr. 1785, but otherwise opposed his measures, voted against his Irish propositions, 13 May 1785, as detrimental to Scottish interests, and against Richmond’s fortifications plan, 27 Feb. 1786. An active committee man, Dundas rarely spoke in the House, and then only on Scottish or Yorkshire concerns.
‘Beloved by men of all parties in Scotland’ for his ‘respectable and independent character’,
