Sir Thomas Kennedy, 9th Earl of Cassilis (bef. 1733 – 30 November 1775) was a Scottish peer, the son of Sir John Kennedy, 2nd Baronet.
He never married.
He succeeded to the title of 4th Baronet Kennedy, of Culzean on 10 April 1744, upon the death of his elder brother. On 29 February 1760 the Court of Session found the right to the estates of the 8th Earl of Cassillis to be in Thomas' favour, after a competition, both for the estates and for the title of Earl of Cassilis, between William Douglas, Earl of March and Ruglen, heir of line, and Sir Thomas, the heir male. The same was found with regard to the title on a reference to the House of Lords, 27 January 1762. He succeeded to the titles of 9th Earl of Cassilis and 11th Lord Kennedy on 27 January 1762. He held the office of Representative Peer (Scotland) between 1774 and 1775.