Gacs started his career as a researcher at the Applied Mathematics Institute of the Hungarian Academy of Science.
Throughout his studies he had the opportunity to visit Moscow State University and work with Andrey Kolmogorov and his student Leonid A Levin.
It was Gács and László Lovász who first brought ellipsoid method to the attention of the international community in August 1979 by publishing the proofs and some improvements of it.
[6] His main contribution and research focus were centered on cellular automata and Kolmogorov complexity.
[9] Gacs authored several important papers in the field of algorithmic information theory and on Kolmogorov complexity.