From 1966-1967 he was a Research Associate at CERN. Returning to CERN in 1970 as Division Leader of the Nuclear Physics Division, he went on to become a member of the Directorate responsible for the Co-ordination of the Experimental Programme.

Chairman of the ISR Committee at CERN (1973-76); he was then elected as a member of the Scientific Policy Committee in 1979.

Following the Léon Van Hove and John Adams' years as Director-General for Research and Executive Director-General, he became the sole Director-General of CERN in 1981, serving eight years in of fice, until Carlo Rubbia succeeded him in January 1989.

Schopper's years as CERN's Director-General culminated in the successful construction of LEP (Large Electron-Positron Collider) with the installation and the first successful tests of the four detectors for the LEP experiments.

In order to make sufficient resources available for the realization of LEP, several facilities had to be closed (notably ISR, BEBC and EHS).

Other highlights during Schopper's office included the awarding of two Nobel Prizes for Physics.

• In 1984 the prize was awarded jointly to Carlo Rubbia and Simon van der Meer for their decisive contributions to the large project which lead to the discovery of the field particles W and Z, communicators of weak interaction.
• In 1988, Jack Steinberger, continuing his research work at CERN, was a joint recipient of the prize (together with Leon M. Lederman and Melvin Schwartz, USA) for the neutrino beam method and the demonstration of the doublet structure of the leptons th rough the discovery of the muon neutrino.