He was born in Chicago, Illinois, on September 15, 1926, to Sophia Zmijewski and Casimir Ignatius Derwinski, who died in 1947.

Derwinski served in the United States Army in the Pacific Theater during World War II and in the postwar U.S. occupation of Japan.

He served 12 terms as a Republican representative from the 4th District of Illinois, a suburban region south and west of Chicago, eventually becoming ranking member of the House Foreign Relations Committee.

Mihailović had received the Legion of Merit for his resistance efforts against the Axis—but this information was marked "secret" at the behest of the State Department so as not to harm relations with Marshal Tito, the current ruler of Yugoslavia in 1967.

On learning of his death, former United States Senator Peter Fitzgerald (R-IL) described Derwinski as "a giant in Illinois politics [...] [H]e had incredible connections in all the different ethnic neighborhoods in Chicago, he was really loved by everybody on both sides".