Jean Zinn-Justin has worked as a theoretical and mathematical physicist at Saclay Nuclear Research Centre (CEA) since 1965, where he was also Head of the Institute of Theoretical Physics (IPhT) from 1993-1998 and Head of Institute for the Fundamental Laws of the Universe (IRFU) from 2003 to 2008. He had a position of Scientific Adviser at IRFU from 2008-2025. He also helds the position of Adjunct Professor at Shanghai University and Honorary Pofessor at Suzhou University. Previously he has served as a visiting professor at the Massachusetts Institute of Technology (MIT), Princeton University, State University of New York at Stony Brook, Harvard University and Heidelberg University. He directed the Les Houches Summer School for theoretical physics from 1987 to 1995.

He has served on editorial boards for several influential physics journals including the French Journal de Physique, Nuclear Physics B, Journal of Physics A, and the New Journal of Physics. He is member of the French Academy of Sciences and the Academy for Sciences and Literature in Mainz (Germany).