Thomas Desmond Williams (26 May 1921 – 18 January 1987) was an Irish academic and Professor of Modern History at University College Dublin (UCD).
His parents were UCD Professor of Education W.J. Williams and Angela Williams (née Murnaghan). His maternal grandfather was George Murnaghan. He attended a primary school run by Dominican nuns and was taught by his father for his secondary education.
At UCD he won scholarships, and in 1942 was awarded the John Brooke memorial scholarship, after which he joined the legal profession. He worked for the British Foreign Office and was a member of British Intelligence during the Second World War.
He became Professor of Modern History at UCD in 1949. In 1953, in a series of articles in the Leader and Irish Press, he accused the war-time Irish Minister to Spain, Leopold Kerney, of having been a Nazi collaborator. Kerney sued him and the two publications for libel. Despite Williams having been supplied with captured German documents by the British Foreign Office to boost his case and Kerney being refused the right to present Irish Ministry documents in support of his action, Kerney won the case, which was settled out of court.