Philip Kerr, 11th Marquess of Lothian

Philip Henry Kerr, 11th Marquess of Lothian, KT, CH, PC, DL (18 April 1882 – 12 December 1940) was a British politician, British Ambassador to the United States and editor of various journals. He was private secretary to Prime Minister David Lloyd George between 1916 and 1921 and as such played a major role in the Paris Peace Conference (1919–1920). After succeeding a cousin in the marquessate in 1930, he held junior ministerial offices in the Lords from 1931 in the National Government, headed by Ramsay MacDonald, until he resigned from it in 1932.

In the 1930s, Lothian promoted entente with Germany, and was considered by critics as a leading advocate of appeasement of Germany but his role was more complex than that. He felt the harshness of the ultimate German reparations in the Treaty of Versailles had been a great mistake. He also emphasised the dangers of Stalin's communism. He changed his mind about Hitler's intentions after reading an English translation of Mein Kampf. He then felt war was inevitable and it was vital that Britain speed up re-armament as their armed forces were no match for Hitler's at the time.

From 1939 to his death, he was Ambassador to the United States. As such he probably did more than any individual, other than the British Prime Minister Winston Churchill, to get a neutral United States finally involved in the Second World War and he proved highly successful in winning America's support for the British war effort, especially the Lend-Lease Act, which passed Congress after his death.

On Lothian's death, Churchill described him as "our greatest ambassador to the United States".