William Erskine, second son of Walter Erskine, 11th Earl of Mar, was educated at Eton College and Magdalen College, Oxford. He joined the Foreign Office in 1894 and served at Buenos Aires, Teheran, Rome and Stockholm where he was chargé d'affaires in 1913. He was posted to Athens with the rank of Counsellor of Embassy 1913–17 where he was British delegate to the international financial commission which had been established following the Greco-Turkish War (1897) to oversee the public finances of Greece. He was Counsellor at Rome 1917–19, Minister to Cuba 1919–21 (and concurrently to Haiti and the Dominican Republic), Minister to Bulgaria 1921–27, and Minister to Poland 1928–29, continuing there as Ambassador 1929–34 after the post was raised from legation to embassy. He was the first ambassador to Poland since the time of King Jan III Sobieski in the seventeenth century.