July 1944, Bradbury, then a Navy commander, transferred to the Los Alamos Laboratory to work on the Manhattan Project, where he headed the implosion field test program. Bradbury was then placed in charge of the assembly of the non-nuclear components of the plutonium implosion weapon for the world's first nuclear explosion at Trinity site in New Mexico on 16 July 1945.
Shortly after the end of World War II in 1945, Bradbury was offered the position of director of the Los Alamos laboratory, at the recommendation of J. Robert Oppenheimer, who had just resigned as director. Though Bradbury had planned to resume teaching at Stanford, he agreed to serve as an interim director for six months.
Uncertainty about the laboratory's future ended with the creation of the Atomic Energy Commission in 1946. Bradbury remained the permanent director at Los Alamos, where he oversaw the continued development and testing of nuclear weapons.
The laboratory expanded its objectives beyond weapons development to take on basic nuclear research and nuclear applications, testing several exploratory reactor designs, including solid and liquid plutonium fuels and gas-cooled uranium reactors. Bradbury also encouraged expansion of the laboratory's research into other areas, such as physics, chemistry, metallurgy, and space technology, as well as establishing programs in biological and medical health research.
Bradbury received numerous awards, including the Department of Defense's Distinguished Public Service Medal in 1966, and the Enrico Fermi Award in 1970. Bradbury retired in 1970, but continued to live in Los Alamos with his family.
Norris Bradbury died on 20 August 1997.