Parisian-born Gennes was educated at the Ecole Normale in his native city, completing his PhD there in 1955. He was appointed professor of solid-state physics at the University of Paris in 1961; since 1971 he has served as professor of physics at the Collège de France and from 1976 as director of the College of Physics and Chemistry, Paris.

Some areas of science have long been thought to be too unstructured and messy to be conducive to traditional physical analysis. Two such areas, liquid crystals and polymers, were consequently largely ignored by physicists. Gennes, however, saw that they behave in many ways just like other better understood physical processes.

Liquid crystals consist of rodlike molecules in a liquid state. They undergo, like magnets and superconductors, phase changes. Thus in what is known as the smetic A phase, the molecules are oriented with their axes perpendicular to the layers; at lower temperatures they adopt the C phase with a parallel orientation. Using concepts derived from the study of phase changes in other fields Gennes was able to throw light on changes in liquid crystals. The results of his work were described in his The Physics of Liquid Crystals (1974). Gennes adopted a similar approach to his study of polymers which he described fully in his Scaling Concepts of Polymer Physics (1979).

For his work in these fields Gennes was awarded the 1991 Nobel Prize for physics.