In 1960 he joined Dames & Moore at their New York Office and worked there until 1962, when returned to California begin his PhD at UC Berkeley.
After earning his PhD, he was a member of the teaching and research staff of the geotechnical engineering group at the University of California, Berkeley (1967-1975).
In 1989, he joined the Department of Civil and Environmental Engineering at University of California, Davis, where he was also Director of the Center for Geotechnical Modeling (CGM) (1989–1996).
[5] He used boring logs and SPT low counts from the 1964 Niigata earthquake to illustrate the use of the Seed-Idriss simplified liquefaction procedure.
[7][8] After the 1989 Loma Prieta earthquake Idriss was appointed to the eleven-member Governor's Board of Inquiry, chaired by George W. Housner, which was formed to study the significant damage to bridges and freeway structures and to make recommendations about how to prevent such damage in the future.