Thomas Dundas of Fingask and Carronhall combined commercial agency, landholding and public office in eighteenth-century Scotland. He worked for his younger brother Lawrence, whose business supplied the British army. This connection offered opportunities beyond their father's struggling Edinburgh business and remained important as Lawrence acquired wealth and political influence. Thomas became a burgess of Edinburgh in 1734 and served as deputy Lord Lyon King of Arms from 1744 to 1754.

He purchased Carronhall in 1749, adding landed status to his commercial interests. His marriage connections also linked the household with established Scottish families. After an earlier marriage, he married Lady Janet Maitland, a daughter of the Earl of Lauderdale. Their children included Thomas, later an army officer, and Charles, who eventually became Baron Amesbury. These family relationships helped place the household within overlapping networks of property, business and public service.

In 1768 Dundas entered Parliament for Orkney and Shetland with his brother's support. He held the seat until December 1770, when he accepted appointment as a police commissioner. His son Thomas entered Parliament for the constituency in 1771. The father's brief parliamentary career should be distinguished from the son's later military campaigns in America and the Caribbean. Dundas remained associated with his Scottish estates until his death in 1786.