In 1968 he completed a doctoral degree there, on multilayer dielectric filters for the ultraviolet, titled Appareillage permettant la réalisation de filtres multidiélectriques UV : Étude des couches Sb2O3.

[7][8] During this time, Agostini worked in the lab of Gérard Mainfray and Claude Manus, where he researched on multiphoton ionization using the powerful lasers there.

[9][10][11] In 2001, Agostini and his team at CEA Saclay along with Harm Geert Muller at the Dutch Foundation for Fundamental Research on Matter (FOM), using an advanced laser at the Laboratoire d'Optique Appliquée [fr], managed to create a train of pulses each 250 attoseconds in duration.

[12][13] Agostini was a visiting scientist at the Brookhaven National Laboratory in the U.S. state of New York between 2002 and 2004, where he worked in Louis F. DiMauro's group.

He was elected a Fellow of OSA in 2008 “for leadership in the development of innovative experiments providing major insights into the dynamics of the nonlinear response of atoms and molecules submitted to strong infrared laser pulses.”[7] In 2023, he received the Nobel Prize in Physics for "for experimental methods that generate attosecond pulses of light for the study of electron dynamics in matter" along with Anne L'Huillier and Ferenc Krausz.