Bardeen, the son of a professor of anatomy, was born in Madison, Wisconsin, and studied electrical engineering at the University of Wisconsin. He obtained his PhD in mathematical physics at Princeton in 1936. Bardeen began work as a geophysicist with Gulf Research and Development Corporation, Pittsburgh, in 1931 but in 1935 entered academic life as a junior fellow at Harvard, moving to the University of Minnesota in 1938. He spent the war years at the Naval Ordnance Laboratory, followed by six creative years from 1945 until 1951 at the Bell Telephone Laboratory, after which he was appointed professor of physics and electrical engineering at the University of Illinois, a post he held until 1975.

Bardeen is remarkable as a recipient of two Nobel Prizes for physics. The first, awarded in 1956, he shared with Walter Brattain and William Shockley for their development of the point-contact transistor (1947), thus preparing the way for the development of the more efficient junction transistor by Shockley.

Bardeen's second prize was awarded in 1972 for his formulation, in collaboration with Leon Cooper and the American physicist John Schrieffer (1931–2019), of the first satisfactory theory of superconductivity – the so-called BCS theory. In 1911 Heike Kamerlingh-Onnes had discovered that mercury lost all electrical resistance when its temperature was lowered to 4.2 K. Superconductivity was also shown to be a property of many other metals, yet despite much effort to understand the phenomenon, a full explanation was not given until 1957. The basic innovation of the BCS theory was that the current in a superconductor is carried not by individual electrons but by bound pairs of them, later known as Cooper pairs. The pairs form as a result of interactions between the electrons and vibrations of the atoms in the crystal. The scattering of one electron by a lattice atom does not change the total momentum of the pair, and the flow of electrons continues indefinitely. The success of the BCS theory led to an enormous revival of interest in both the theory of superconductors and their practical application.