[1] His parents were American-born linguist Pearl Beaglehole (née Malsin) and her husband Ernest Beaglehole, a psychologist and ethnologist, who had met while they were both studying at the London School of Economics.
[1][2] Educated at Wellington College from 1951 to 1954,[3] he then studied physics, chemistry and psychology at Victoria University College, graduating with a Bachelor of Science in 1958 and a Master of Science with first-class honours in 1960.
[1][4] He then carried out doctoral research into the optical properties of copper and gold in the far ultraviolet at Trinity College, Cambridge under Tom Faber, and was awarded his PhD in 1963.
[1] He had three children with his wife Ann Beaglehole; after their marriage ended, he had another child with his long-term partner Bhagee Ramanathan.
[1] He also developed an improved ellipsometric method for measuring the thickness of liquid interfaces, which led to the establishment of Beaglehole Instruments in 1993.