Between 1940 and 1944, he gained national prominence as chairman of the Truman Committee, which was aimed at reducing waste and inefficiency in wartime contracts. Truman was elected vice president in the 1944 presidential electionand assumed the presidency upon Roosevelt's death in April 1945.

Truman felt even more comfortable with President Johnson, with whom he had enjoyed cordial relations while Johnson was on Capitol Hill. He never got along with President Nixon, however. Truman found time to relax and rest in his post-presidential years.

Truman mostly presided over the Senate and attended parties and receptions. He kept the same offices from his Senate years, mostly only using the Vice President's official office in the Capitol to greet visitors. Truman was the first vice president to have a Secret Service agent assigned to him.

In 1945, he was made a 33° Sovereign Grand Inspector General and an Honorary Member of the supreme council at the Supreme Council A.A.S.R. Southern Jurisdiction Headquarters in Washington D.C.Truman was also a member of Sons of the American Revolution(SAR)and a card-carrying member of the Sons of Confederate Veterans.