Connally served in the United States Navy during World War II, first as an aide to James V. Forrestal, then as part of the planning staff for the invasion of North Africa by General Dwight D. Eisenhower.
On his release from the navy, Connally practiced law in the Alvin Wirtz law firm, until Lyndon Baines Johnson, then a newly elected senator, persuaded him to return to Washington, D.C. to serve as a key aide.