Working with mathematician Richard Q. Twiss, astronomer R. Hanbury Brown invented the optical intensity interferometer, a telescopic device that allowed astronomers to study stars that until then had been little more than flickers of light, even as mathematicians, physicists, and other experts scoffed that such a device was physically impossible.

Early in his career, Brown worked with Robert Watson-Watt on the secret development of radar, then headed a group that developed a shorter-wavelength radar for use in aircraft. After World War II, he worked with Bernard Lovell at Jodrell Bank Observatory. His research showed that cosmic radio waves emanate from the Andromeda spiral galaxy, leading to the modern understanding of quasars -- "quasi-stellar objects", and he devised methods for minimizing background noises that had plagued early radio astronomy. His autobiography is titled Boffin, an Australian colloquialism with a meaning somewhere between "geek" and "egghead". His grandfather, also named Robert Hanbury Brown, was knighted for his extensive work and writings on irrigation.

In March, 1960 he was elected a Fellow of the Royal Society of London and in 1971 was awarded their Hughes Medal for " his efforts in developing the optical stellar intensity interferometer and for his observations of Spica". In 1968, he received the Eddington Medal jointly with Twiss (see Hanbury Brown and Twiss effect). He also won the Thomas Ranken Lyle Medal of the Australian Academy of Science in 1972. In 1982 he was named President of the International Astronomical Union, a title he retained until the end of his term in 1985. In 1986 he was made a Companion in the Order of Australia. He was awarded the Albert A. Michelson Medal of the Franklin Institute in 1982, jointly with Richard Q. Twiss.