Jan S. Nilsson was head of ICTP's Office of External Activities from 1985 to 1988, and a former member of the Centre's Scientific Council from 1996 to 2003. He attended the first workshop at Miramare, Trieste that preceded the founding of ICTP in 1964. He was an associate fellow of the Academy of Sciences for the Developing World, as well as president of the International Union of Pure and Applied Physics (IUPAP).

One of Sweden's leading physicists, Nilsson was a professor of mathematical physics at Chalmers University of Technology, the dean of the Faculty of Mathematics at the University of Gothenburg, and for six years rector at the same university.

In addition, Nilsson was president of the board of directors of the Wallenberg foundation, which is Sweden's largest private funding agency for research and advanced scientific equipment.