A graduate of the U.S. Naval Academy at Annapolis, Md., in 1904, Halsey served as a destroyer commander in World War I. He became a naval aviator in 1935 and reached the rank of vice admiral in 1940. After the Japanese attack on Pearl Harbor (December 1941), Halsey's task force was virtually the only operational battle group left in the Pacific. While the United States rebuilt its fleet, he directed surprise forays on Japanese-held islands in the Marshalls and Gilberts as well as on Wake Island. In April 1942 his group maneuvered close enough to Tokyo for Lieutenant Colonel James Doolittle (Doolittle, James H.)'s planes to carry out the first bombing of the Japanese capital. Consistent successes led to his appointment in October 1942 as commander of the South Pacific force and area. During the next two months, he played a vital role in the Battle of Santa Cruz Islands and the naval Battle of Guadalcanal (November 12–15) and was promoted to admiral. From 1942 to mid-1944 Halsey directed the U.S. campaign in the Solomon Islands.

In June 1944 Halsey became commander of the 3rd Fleet and led his carrier task force in brilliant air strikes. He was responsible for covering and supporting U.S. land operations as well as finding and destroying much of the Japanese fleet in the Battle of Leyte Gulf (Leyte Gulf, Battle of) (October). He led U.S. forces in the final naval operations around Okinawa in the Ryukyu Islands from May 28, 1945, to September 2, when the Japanese surrendered.

Halsey was promoted to the rank of fleet admiral in December 1945, and he retired in 1947. He was president of International Telecommunications Laboratories (1951–57).