Detecting this small variability by the Doppler effect had been possible thanks to the development of a new type of spectrograph, ELODIE,[13] installed at the Haute-Provence Observatory, combined creative approach to measuring precise stellar radial velocity.

Over the next 25 years, Didier Queloz's main scientific contributions have essentially been focused to expand our detection and measurement capabilities of these systems to retrieve information on their physical structure.

He published a reference paper describing how to disentangle stellar activity from a planetary signal using proxies, including new algorithms that have become standard practice in all planet publications based on precise Doppler spectroscopy data.

Queloz received the 2011 BBVA Foundation Frontiers of Knowledge Award of Basic Sciences (co-winner with Mayor) for developing new astronomical instruments and experimental techniques that led to the first observation of planets outside the solar system.

HARPS performances, allied with the development of a new analysis software inherited from all past experiences gathered with ELODIE and CORALIE, would considerably improve the precision of the Doppler technique.

The pinnacle of this program would be reached 10 years later, after he led a significant upgrade of CORALIE, and established a collaboration with the Wide Angle Search for Planets (WASP) consortium in the UK.

In 2003 Didier Queloz, recently appointed at a faculty position, with his research team pioneered and established the combination of these techniques by first measuring bulk density of OGLE transiting planets.

In the course of this program and a collaboration with his Colleague S. Zucker from Tel-Aviv University, they developed the mathematical foundation to compute residual noise they encountered during the analysis of transit they were trying to model.

In the European context, he is leading at Geneva (through his joint Professor appointment) the development of the ground segment CHEOPS[19] space mission and he chairs the science team.

This program, carried out in collaboration with M. Gillon from the University of Liège, is at the origins of the detection of TRAPPIST-1, a planetary system potentially interesting to further search for atmosphere and life signature.

In parallel to his research and teaching activities, Didier Queloz has participated in numerous documentaries, movies, articles, and TV and radio interviews to share the excitement, and to explain results and promote interest in science in general.

[21] In October 2019, related to his work in astronomy and exoplanet discoveries, Queloz predicted humans will discover extraterrestrial life in the next 30 years, stating, "I can't believe we are the only living entity in the universe.

"[22] In December 2019, Queloz took issue with those who are not supportive of helping to limit climate change, stating, “I think this is just irresponsible, because the stars are so far away I think we should not have any serious hope to escape the Earth [...] Also keep in mind that we are a species that has evolved and developed for this planet.