Štefan Osuský (31 March 1889 – 27 September 1973) was an Austro-Hungarian born Slovak lawyer, diplomat, politician and university professor.

When in February 1910 protesting American Slovaks disrupted Apponyi's speech in Chicago, the count with distaste replied that he "has nothing to say to people such as [Osuský]".

Immediately after his arrival in the United States he began working actively in expatriate organizations, at first in the Czech National Association, later in the Slovak League in the US.

In Paris he started to cooperate with the Czechoslovak National Council, whose objective was the dissolution of Austria-Hungary and the creation of a new state for Czechs and Slovaks.

In 1918 he helped organize the Czechoslovak Legions in Italy, established in spite of international treaties prohibiting the creation of military units out of captured enemies.

"[2] He significantly contributed to the functioning of the newly formed League of Nations; between 1921 and 1932 he worked with the Reparations Commission, representing not only Czechoslovakia but also Poland, Yugoslavia, Romania and Greece.

From 1921 Osuský worked as the Czechoslovak ambassador in France, contributing significantly to the development of Czechoslovak-French relations, a cornerstone of ČSR's international security.

2 October 1939 Osuský signed an Agreement on the Reestablishment of the Czechoslovak Army in France with French Prime Minister Édouard Daladier.

The epitaph on his grave, quoting Psalm 1:3, reads: "And he shall be like a tree planted by the rivers of water, that bringeth forth his fruit in his season; his leaf also shall not wither."