Born in Paris to a respected Polish family, Kosciusco earned a degree in ethics and sociology from the École normale supérieure and taught high school in Grenoble from 1941 to 1943.
He escaped, joined the French Resistance, and participated in the defense of the city hall of Paris in 1944,[citation needed] for which he was decorated after the war.
[citation needed] He was made deputy director of the cabinet of Léon Blum in 1946, and then Chief of Staff (Civil) for President Vincent Auriol in 1947, a position he held until 1954.
[citation needed] Kosciusko's international standing rose when he was France's delegate to the United Nations General Assembly from 1957 to 1962.
He was the national secretary for foreign relations of the Rally for the Republic party from 1983 to 1988, and was mayor of Saint-Nom-la-Bretèche from 1977 until his death in Paris in 1994.