De Broglie was descended from a French family ennobled by Louis XIV. He was born in Dieppe, France, and educated at the Sorbonne. Originally a historian, he became interested in science in World War I when he was posted to the Eiffel Tower as a member of a signals unit. He pursued this interest after the war and finally obtained his doctorate in physics from the Sorbonne in 1924. He taught there from 1926, serving as professor of theoretical physics at the newly founded Henri Poincaré Institute (1928–62).

De Broglie is famous for his theory that particles (matter) can have wavelike properties. At the start of the 20th century physicists explained phenomena in terms of particles (such as the electron or proton) and electromagnetic radiation (light, ultraviolet radiation, etc.). Particles were ‘matter’ – conceived as discrete entities forming atoms and molecules; electromagnetic radiation was a wave motion involving changing electric and magnetic fields.

In 1905 two papers by Albert Einstein began a change in this conventional view of the physical world. His work on the special theory of relativity led to the idea that matter is itself a form of energy. More specifically he explained the photoelectric effect by the concept that electromagnetic radiation (a wave) can also behave as particles (photons). Later, in 1923, Arthur Compton produced further evidence for this view in explaining the scattering of x-rays by electrons.

In 1924 de Broglie, influenced by Einstein's work, put forward the converse idea – that just as waves can behave as particles, particles can also behave as waves. He proposed that an electron, for instance, can behave as if it were a wave motion (a de Broglie wave) with wavelength h/p, where p is the momentum of the electron and h is Planck's constant. This revolutionary theory was put forward in de Broglie's doctoral thesis. Experimental support for it was obtained independently by George Thomson and by Clinton J. Davisson and the wavelike behavior of particles was used by Erwin Schrödinger in his formulation of wave mechanics.

The fact that particles can behave as waves, and vice versa, is known as wave–particle duality and has caused intense debate as to the ‘real’ nature of particles and electromagnetic radiation (see Niels Bohr, Max Born, Erwin Schrödinger). De Broglie took the view that there is a true deterministic physical process underlying quantum mechanics – i.e. that the current indeterminate approach in terms of probability can be replaced by a more fundamental theory. He based his ideas on the concept of particles that are concentrations of energy guided through space by a real wave, and exchanging energy with a ‘subquantum medium’.

De Broglie received the 1929 Nobel Prize for physics for his “discovery of the wave nature of the electron.”