Thomas Cornwallis (c. 1605–1675), was an English politician and colonial administrator. Cornwallis served as one of the first Commissioners of the Province of Maryland (Proprietary Colony of Maryland) and Captain of the colony’s military during the early years of settlement. In 1638, in a naval engagement with Virginian colonists, he captured Kent Island for Maryland.
Thomas was probably the grandson, or possibly the second son (undocumented) of Sir Charles Cornwallis of Beeston, Norfolk (d. 1629), an ambassador to Spain and brother of Elizabeth Cornwallis and Sir William Cornwallis of Brome, the direct ancestor of Charles Cornwallis, 1st Marquess Cornwallis. Thomas was probably the son (or brother) of the author William Cornwallis.
As the second son, he could not hope to inherit his father’s land. The Cornwallis family were Roman Catholic Recusants and therefore George Calvert's project of an autonomous colony in the New World for English Catholics appealed to him. In 1634 he accompanied Leonard Calvert to what was then Virginia and became a Commissioner to the Governor. This put him in a powerful advisory position to Leonard Calvert.