Sir George William Buchanan, GCB, GCMG, GCVO, PC (25 November 1854 – 20 December 1924) was a British diplomat. Born in Copenhagen, Denmark, he was the youngest son of Sir Andrew Buchanan, 1st Baronet, diplomat and Frances, daughter of Very Rev Edward Mellish by Elizabeth Leigh.
Buchanan entered diplomatic service in 1876, and served as Second Secretary in Tokyo, Vienna and Bern, and as Secretary in Rome. By 1899 he was serving on the Venezuelan Boundary Commission, and later that year he was appointed Chargé d'affaires at Darmstadt and Karlsruhe. In late 1901 he moved to Berlin, where he was appointed First Secretary at the British embassy. From 1903 to 1908 he was Envoy Extraordinary and Minister Plenipotentiary to Bulgaria, and in 1909 he was appointed as Minister to the Netherlands and Luxembourg. Invested with the Knight's Grand Cross of Royal Victorian Order in 1909, he was next sworn to the Privy Council In 1910 Buchanan was appointed as the British Ambassador to Russia. He kept abreast of the political developments in Russia and met some of the leading liberal reformists in the country.
When the Dardanelles were guaranteed by Germany to the Turks, Italy sent two secret documents vis the British diplomatic corps from Sir Michael Rodd to Sir George at St Petersburg. In it were the evidence that Russia needed to persuade Italy to support her Serbian policy in the Balkans. On 4 March 1915 Imperiali, the Italian envoy to London had presented the documents to Sir Edward Grey on an authority of 16 February from Sonnino, their foreign minister. France attached great importance to Italy's decision to join the allies. Buchanan was able to bring Count Sazonov to the negotiating table.