Ladefoged was involved with the phonetics laboratory at UCLA, which he established in 1962. He also was interested in listening to and describing every sound used in spoken human language, which he estimated at 900 consonants and 200 vowels. This research formed the basis of much of The Sounds of the World's Languages. In 1966 Ladefoged moved from the UCLA English Department to join the newly established Linguistics Department.
While at UCLA, Ladefoged was hired as a consultant on the movie My Fair Lady. He wrote the transcriptions that can be seen in Professor Higgins's notebook, and his voice was used in the scenes where Higgins describes vowel pronunciation.
Ladefoged married Jenny MacDonald in 1953, a marriage which lasted over 50 years. They had three children: Lise Friedman, a bookseller; Thegn Ladefoged, archaeologist and professor of anthropology at University of Auckland; and Katie Weiss, attorney and public defender, residing in Nashville, Tennessee. He also had five grandchildren Zelda Ladefoged, Ethan Friedman, Amy Friedman, Joseph Weiss, and Catherine Weiss.
On May 5, 1970, Ladefoged was arrested and suffered injuries from police while participating in an anti–Vietnam War protest at UCLA. He was initially charged with failure to disperse, but the charge was later changed to assault on a police officer. He was acquitted in the first trial.
Ladefoged died on 24 January 2006 at the age of 80 in hospital in London, England after a research trip to India. He was on his way home to Los Angeles, California from his research trip.
1953–55: Assistant Lecturer in Phonetics, University of Edinburgh
1955–59: Lecturer in Phonetics, University of Edinburgh
Ladefoged (1962). The nature of vowel quality. Monograph supplement to Revista do Laboratório de Fonética Experimental da Faculdade de Letras da Universidade de Coimbra (Journal of Experimental Phonetics Laboratory of the Faculty of Arts, University of Coimbra).
Ladefoged (1962). Elements of acoustic phonetics. University of Chicago Press. ISBN 0-226-46764-3. Paperback edition 1971. Translation into Japanese, Taishukan Publishing Company, 1976. Second edition, with added chapters on computational phonetics 1996.
Ladefoged (1964). A phonetic study of west African languages. Cambridge: Cambridge University. ISBN 0-521-06963-7. Reprinted 1968.
Ladefoged (1967). Three areas of experimental phonetics. London: Oxford University Press. ISBN 0-19-437110-7.
Ladefoged, Peter; Ruth Glick; Clive Criper (1969). Language in Uganda. Nairobi: Oxford University Press. ISBN 0-19-436101-2.
Ladefoged (1971). Preliminaries to linguistic phonetics. Chicago: University of Chicago Press.
Ladefoged (1975). A course in phonetics. Orlando: Harcourt Brace. ISBN 0-15-507319-2. 2nd ed 1982, 3rd ed. 1993, 4th ed. 2001, 5th ed. Boston: Thomson/Wadsworth 2006, 6th ed. 2011 (co-author Keith Johnson) Boston: Wadsworth/Cengage Learning. Japanese translation 2000.