His grandfather, Dimitris Nakas, was an Aromanian and an ardent Greek nationalist who had migrated at the beginning of the 20th century to New York, but in March 1914 traveled back to his native land in order to participate in the Greek struggle for northern Epirus, and died in 1916; Nanopoulos' father was born nine months prior.

[2] His mother, Vasiliki Korasidi, was born in Kifissia but descended from the Greek island of Kea.

In 1997 he was appointed regular member of the Academy of Athens, and, in 2005, President of the Greek National Council for Research and Technology, Greek National Representative to the European Laboratory for Particle Physics, CERN, and to the European Space Agency (ESA).

He is one of the principal developers of the flipped SU(5) model, first proposed by Stephen M. Barr in a paper published in 1982.

[9] On 28 September 2009, he was awarded the 2009 Enrico Fermi Prize from the Italian Physical Society in recognition of his pioneering work in the field of string theory.