A physics professor at Harvard University for most of his career, Ramsey also held several posts with such government and international agencies as NATO and the United States Atomic Energy Commission.

[1] His father, who was of Scottish descent, was a 1905 graduate of the United States Military Academy at West Point and an officer in the Ordnance Department who rose to the rank of brigadier general during World War II, commanding the Rock Island Arsenal.

[1][5] Columbia awarded him a Kellett Fellowship to Cambridge University, where he studied physics at Cavendish Laboratory under Lord Rutherford and Maurice Goldhaber, and encountered notable physicists, including Edward Appleton, Max Born, Edward Bullard, James Chadwick, John Cockcroft, Paul Dirac, Arthur Eddington, Ralph Fowler, Mark Oliphant and J. J. Thomson.

[1][7] Soon after Ramsey arrived at Columbia, Rabi invented molecular-beam resonance spectroscopy, for which he was awarded the Nobel Prize in Physics in 1944.

[8] Ramsey was part of Rabi's team that also included Jerome Kellogg, Polykarp Kusch, Sidney Millman and Jerrold Zacharias.

Ramsey worked with them on the first experiments making use of the new technique and shared with Rabi and Zacharias in the discovery that the deuteron was a magnetic quadrupole.

[1] In September 1940 the British Tizard Mission brought a number of new technologies to the United States, including a cavity magnetron, a high-powered device that generates microwaves using the interaction of a stream of electrons with a magnetic field, which promised to revolutionize radar.

Ramsey returned to Washington in late 1942 as an adviser on the use of the new 3 cm microwave radar sets that were now coming into service,[7] working for Edward L. Bowles in the office of the Secretary of War, Henry L. Stimson.

Ramsey agreed to do so, but the intervention of the project director, Brigadier General Leslie R. Groves Jr., was necessary in order to prise him away from the Secretary of War's office.

[16] Ramsey supervised the test drop program, which began at Dahlgren, Virginia, in August 1943, before moving to Muroc Dry Lake, California, in March 1944.

[18] Ramsey drew up tables of organization and equipment for the Project Alberta detachment that would accompany the USAAF's 509th Composite Group to Tinian.

During the 1950s, he was the first science adviser to NATO and initiated a series of fellowships, grants and summer school programs to train European scientists.

[1][6][21] Ramsey's research in the immediate post-war years looked at measuring fundamental properties of atoms and molecules by use of molecular beams.

[22] He was awarded the Nobel Prize in Physics in 1989 "for the invention of the separated oscillatory fields method and its use in the hydrogen maser and other atomic clocks".

However, he remained active in physics, spending a year as a research fellow at the Joint Institute for Laboratory Astrophysics (JILA) at the University of Colorado.

[28] In 2004, he signed a letter along with 47 other Nobel laureates endorsing John Kerry for President of the United States as someone who would "restore science to its appropriate place in government".