Sir Charles Kingsley Webster KCMG (25 July 1886 – August 1961) was a British historian and diplomat.
He was educated at the Merchant Taylors' School, Crosby and King's College, Cambridge.
While Professor of International Relations at the University of Wales, Aberystwyth he wrote his two major books on the foreign policy of Lord Castlereagh, the first (published in 1925) covering the period 1815–1822, the second (published in 1931) that from 1812–1815. In 1932 Webster moved to the newly established Stevenson chair of international relations at the London School of Economics (LSE).
During World War II, he worked extensively in the Foreign Office, especially in the United States, and was a leading supporter of the new United Nations, as he had been of the League of Nations. He attended the first meetings of both the General Assembly and the Security Council in January 1946 and the final meeting of the League of Nations in April. He was made a Knight Commander of the Order of St Michael and St George in the new year's honours list of 1946.
In 1948, Webster gave the Ford Lectures in the University of Oxford. In 1951, his biography of Henry John Temple, 3rd Viscount Palmerston was finally published. He was President of the British Academy in 1950. He was awarded honorary degrees from Oxford, Wales, Rome, and Williams College, Massachusetts, as well as an honorary fellowship at King's College, Cambridge. He retired from his chair at the LSE in 1953.