Which U.S. president was in office when Japan’s surrender was formally signed in 1945?

The U.S. president in office when Japan’s surrender was formally signed in 1945 was Harry S. Truman.

Truman became president on 12 April 1945, after Franklin D. Roosevelt died during his fourth term. By the time Japan formally surrendered on 2 September, Truman had been president for less than five months. His administration directed the final U.S. wartime decisions in the Pacific and began planning the postwar occupation of Japan.

Truman announced the Japanese government’s acceptance of the Allied surrender terms in a radio address to the American people on 14 August 1945. Because of time-zone differences, celebrations occurred on different calendar dates in various countries. Truman reserved the formal designation of V-J Day for the signing ceremony rather than the earlier announcement.

The surrender document was signed aboard USS Missouri in Tokyo Bay. Truman did not attend the ceremony in person, but his administration approved the arrangements and the occupation policy that followed. He later supported the creation of a peace settlement and the rebuilding of Japan under Allied supervision.