Lomnitz was the founding director of the Instituto de Geofísica at the Universidad de Chile. He then taught at the University of California-Berkeley between 1964 and 1968, and moved to the Universidad Nacional Autónoma de México's Instituto de Geofísica in 1968, where he worked for the rest of his life. He founded Mexico's first seismic network, RESMAC, in 1971, and became editor of the journal Geofísica Internacional in 1990. Lomnitz authored a number of books, notably Global Tectonics and Earthquake Risk (Elsevier, 1974).