Rendel then entered the Diplomatic Service. He was head of the Eastern Department of the Foreign Office, 1930-1938. In 1922 he produced a seven-page British Foreign Office document which detailed the persecution of Greeks and other minorities in the Ottoman Empire. The document drew on official reports and eyewitness testimonies by personnel who were present. Rendel stated that throughout the First World War, "...it is generally agreed that about 1,500,000 Armenians perished in circumstances of extreme barbarity, and that over 500,000 Greeks were deported, of whom comparatively few survived." Rendel then went on to describe further massacres and deportation of Greeks in the period after the Armistice. In 1937 he and his wife Geraldine crossed Arabia. His wife, Geraldine, was the first European woman to be received for dinner at the royal palace in Riyadh. Rendel said of Riyadh: Whilst Rendel was His Britannic Majesty's Envoy Extraordinary and Minister Plenipotentiary to Bulgaria, the United Kingdom broke off diplomatic relations as the country was now under the control of the Nazis. It fell to Rendel to take his staff of 50 by train to Istanbul, in Turkey. His party was caught in a huge bomb explosion at the Pera Palace Hotel. Rendel was upstairs when the bomb in the baggage room exploded with devastating consequences. His daughter Ann, then 21 and acting as Legation Hostess, was knocked down and slightly injured. In all there were four deaths and 30 injured. It was later claimed by the Germans that various bombs had been placed in the Legation's luggage before it left Sofia. In 1941, he was appointed Envoy Extraordinary and Minister Plenipotentiary to the Kingdom of Yugoslavia, a post held until 1943. He was knighted in the latter year and served as Ambassador to Belgium between 1947 and 1950. Rendel headed a Commission in 1953 to recommend further changes in the constitutional system that helped created the Constitution of Singapore under the Singapore Colony Order in Council 1955. Rendel also served on various UN committees. Though officially retired, he continued to be employed by the Foreign Office until 1964.
Personal
Rendel had two sons and two daughters with his wife Geraldine. His wife died in 1965.
