Born and educated in Austrian Poland, Sikorski served in the Austrian Army. In 1908 he founded a secret Polish military organization, in which Józef Piłsudski (Piłsudski, Józef) was also prominent. During World War I, Sikorski was war commissioner of the Polish Legion, which served with the Austrian Army against Russia. He later distinguished himself in the Polish–Soviet War (1920–21), and in 1921 he was named chief of the Polish general staff.

In 1922–23 Sikorski served briefly as prime minister of Poland. In 1924–25, as minister of military affairs, he guided the modernization of the army. Sikorski remained neutral during Piłsudski's 1926 take-over of the government; but he joined the anti-Piłsudski opposition in 1928, after being dismissed from his command.

When the Germans overran Poland in 1939, Sikorski became prime minister of the government in exile, establishing good relations with Allied leaders. But in the later course of World War II the Soviet dictator Stalin broke off Soviet–Polish diplomatic contact in April 1943, using as pretext Sikorski's request that the International Red Cross investigate the murder at Katyn (Katyn Massacre) of thousands of Polish officers previously in Russian hands. Sikorski was killed in an air crash at Gibraltar the following July; many have speculated that his death was caused by foul play.