Didier Queloz (born February 23, 1966) is an astronomer with a prolific record in finding extrasolar planets in the Astrophysics Group of the Cavendish Laboratory, Cambridge, and also at the University of Geneva.

Didier Queloz was a Ph.D. student at the University of Geneva when he and Michel Mayor discovered the first exoplanet around a main sequence star. Queloz performed an analysis on 51 Pegasi using radial velocity measurements (Doppler spectroscopy), and was astonished to find a planet with an orbital period of 4.2 days. He had been performing the analysis as an exercise to hone his skills. The planet, 51 Pegasi b, challenged the then accepted views of planetary formation, being a hot Jupiter or roaster. He has received the 2011 BBVA Foundation Frontiers of Knowledge Award of Basic Sciences (co-winner with Michel Mayor) for developing new astronomical instruments and experimental techniques that led to the first observation of planets outside the solar system.