Michaël Gillon is the scientific leader of the exoplanets part of the TRAPPIST project, which has participated to the detection of more than one hundred transiting exoplanets, including the now famous exoplanetary system TRAPPIST-1, revealed to the public on 22 February 2017 during an international press conference at NASA headquarters and through a publication in the scientific journal Nature.

In 2007, Michaël Gillon performed the first detection of the transit of an exoplanet similar to Neptune in terms of mass and radius. In 2010, he was the principal investigator of the project that made the first measurement of the thermal emission of a "super-Earth". Since 2012, he has been developing and leading the SPECULOOS project that targets nearby ultra-cold red dwarfs to detect potentially habitable planets well-suited for detailed atmospheric studies, including the search for chemical traces of life. He is also involved -as executive Board member- in the CHEOPS space mission, which consists in a small space telescope aiming to study in more detail already known transiting planets.