He is best remembered as a Royal Yugoslav ambassador to the United States of America in Washington, D.C., during the most crucial time for the young European kingdom prior to and during the Second World War.

At the Paris Peace Conference, he was secretary of the Delegation of the Kingdom of Serbs, Croats, and Slovenes,[7][8] and then worked in the office of Foreign Minister Ante Trumbić until the end of July 1920.

The Minister of Foreign Affairs, Nikola Pašić, intended to appoint him the first diplomatic official in Geneva in order to maintain constant contact with the General Secretariat of the League of Nations, but he soon gave up that intention,[4][10] and remained in office for the next three years.

The Minister of Foreign Affairs, Momčilo Ninčić, elected him the Secretary-General of the delegation of the Kingdom of Serbs, Croats, and Slovenes at the 5th session of the Assembly of the League of Nations in 1924.

[13] The new Minister of Foreign Affairs, Ninko Perić, decided, in February 1927, to appoint him as a permanent delegate of the Kingdom of Serbs, Croats, and Slovenes to the League of Nations in Geneva.

One of the most difficult tasks he worked on was the Yugoslav lawsuit before the Council of the League of Nations against Hungary for its involvement in the assassination of King Alexander I Karadjordjević at Marseilles in 1934.

[18][19] After the arrival of Milan Stojadinović at the head of the Ministry of Foreign Affairs, in June 1935, the transfer of Konstantin Fotić as a deputy in Warsaw was planned.

He vehemently opposed this proposal, believing that in that way he was set back in the service and publicly humiliated, demanding that he be transferred to London, Paris or Washington, D.C.

His activities gained more weight since 1939, when the United States was much more interested in the development of the military situation in Europe, especially after their entry into World War II.