[2] Efstathiou was educated at Tottenham Grammar School which he left at age 16 and to which he returned as a lab technician.
[3] Efstathiou was a research assistant in the Astronomy Department of University of California, Berkeley from 1979 to 1980, then moved to the Institute of Astronomy at the University of Cambridge, holding research fellowships at King's College, Cambridge from 1980 to 1988.
[4] Efstathiou has made a number of notable contributions to research in cosmology, including: He was awarded the Maxwell Medal and Prize of the Institute of Physics in 1990.
In 1994 he was both appointed a Fellow of the Royal Society (FRS), and was awarded the Bodossaki Foundation Academic and Cultural Prize for Astrophysics.
[9] In 2022 Efstathiou was awarded the Gold Medal of the Royal Astronomical Society, its highest honour, whose previous recipients include Albert Einstein, Edwin Hubble and Fred Hoyle.