[citation needed] Peter Jenni participated in CERN experiments at the Synchro-Cyclotron (1972/3), at the Proton Synchrotron (1974/6), and as ETHZ Research Associate at the Intersecting Storage Rings (ISR) (1976/7), the first high-energy hadron collider.

From 1976 to 1977 Research Associate at the Swiss Federal Institute of Technology in Zürich (ETHZ) working in the CERN-ETH-Saclay collaboration R702 at the CERN Intersecting Storage Rings (P. Darriulat, B. Richter).

In SLAC he also worked on operating the liquid-argon calorimeter for the MARK II experiment where his interest in high-performance calorimetry was developed.

He became a CERN staff member in 1980 working with the UA2 experiment at the Super Proton Synchrotron collider (major involvement in the discoveries of jets and the W and Z bosons).

Early involvement as convener of the jet study group at the ECFA-CERN LHC workshop 1984 (Lausanne, Geneva), member of the advisory panel on the physics potential and the feasibility of experiments at the multi-TeV energies (La Thuile workshop 1987), and calorimetry overview at the ECFA study week on instrumentation technology for high-luminosity hadron colliders (Barcelona 1989).

In 1995, after formal approval of the ATLAS project, he was elected Spokesperson of the experiment, which today comprises some 3000 scientists representing 183 Institutions from 38 countries.

[9] After his retirement as a CERN Senior Research Staff end of April 2013, Peter Jenni has become a Guest Scientist and Honorary Professor with the Albert-Ludwigs-Universität Freiburg, keeping his full engagement with the ATLAS experiment.

He has authored and co-authored many review articles about the LHC project, the Higgs boson discovery, and the history of hadron colliders, for example in 2021 in the CERN Courier.

– Final two years of the ISRC, CERN (1982 and 1983) – Four years LEPC, CERN (1986–1990) – Almost five years PRC of DESY as referee on the HERA experiment calorimetry, DESY, Hamburg, Germany (1984–1989) – First few years of SSC PAC, Dallas, U.S. (1989–1991) – Joint Institute for Nuclear Research (JINR) Dubna Scientific Council (2008–2018) – Served, and still serves, in numerous advisory boards at institute, national, and international levels, in particular for the future HEP projects – During 2012 and 2013 he was strongly involved in shaping the scientific input with the Preparatory Group for the Update of the European Strategy for Particle Physics, personally motivated to promote CERN's future at the high energy frontier – He was a member of High Level Strategy Group of the first Latin American Strategy Forum for Research Infrastructures during 2019 – 2020, and since 2021 he is assuming a consulting role in the first African Strategy for Fundamental and Applied Physics Peter Jenni is frequently invited to give public lectures on experimental particle physics at the LHC.