Grujić is sent as attaché to Serbia's embassy in Constantinople, then to Athens as Chargé d'affaires. A few years later Grujić is sent to represent the Serbian Kingdom in Petrograd. In early October 1908, during the Bosnian Crisis, he is Chargé d'affaires in London, when the Dual Monarchy of Austria-Hungary announced the annexation of Bosnia and Herzegovina. One of Grujić proposal, attached to the protest of the Serbian government, was the concession of a railway to the Adriatic coast, and on the Bosnian side, a revision of the Serbian frontier. On the eve of the First World War, Grujić is secretary-general of the Serbian ministry of Foreign Affairs, on 30 June he met with the Austro-Hungarian secretary of the Habsburg legation in Belgrade, Wilhelm Ritter von Storck, about the Sarajevo assassinations. On 23 July 1914, in the absence of Nikola Pašić, Grujić and acting prime ministerLazar Paču receive from Austrian minister Baron Wladimir Giesl von Gieslingen the ultimatum of Austria-Hungary, Slavko Grujić was one of the main contributors of the reply to the Austrian note. According to Christopher Clark the Serbian reply was "a masterpiece of diplomatic equivocation", Baron Alexander von Musulin, Austria's special envoy, who had written the first draft of the ultimatum, described it as ‘the most brilliant specimen of diplomatic skill’ that he had ever encountered. After the great retreat Slavko Grujić organized the transfer of refugees from the Albanian coast to Corfu and to France. In 1916 he became the first Serbian Ambassador to Switzerland where together with Mable he actively organised humanitarian help to occupied Serbia with the International Committee of the Red Cross in Geneva. On 13 January 1919, Slavko Grujić becomes the first ambassador of the Kingdom of Serbs, Croats and Slovenes, ie the Kingdom of Yugoslavia, in Washington a position he held until 1922. Upon his return to the country, he actively participated in the work of various humanitarian societies. In 1934, after the death of King Alexander I, he became marshal of the court of the young King Peter II of Yugoslavia. In 1935 Grujić was appointed Envoy Extraordinary and Minister Plenipotentiary at the Court of St. James ie ambassador to the United Kingdom, and at the same time to the Netherlands. He died in London of heart failure on 24 March 1937.
Personal life
In 1901, at a ball at the American embassy in Athens, he met his future wife, 21-year-old American archeologist, Mabel Dunlop, they married and returned to Belgrade where he became secretary to the Serbian Cabinet. During the Great War, Mabel organised fundraisings in America for Serbia crossing the ocean more than twenty times by steamer, she founded the Serbian Hospital Fund and a baby hospital in Niš. After the war, Mabel and Slavko Grujić managed to receive $100,000 from the Carnegie Foundation in 1920, in order to build the University Library Svetozar Markovic. According to Barbara Tuchman, Mable Grujić was also recruiting agents for the British Naval Intelligence during the first and second world war.
