Lernoux was born into a comfortable Catholic family in California and excelled in school. She enrolled in the University of Southern California in the late 1950s and, after being nominated to Phi Beta Kappa, qualified as a journalist for the United States Information Agency (USIA), a government arm devoted to promoting U.S. policy overseas. Lernoux began working in Latin America in 1961, just before the Second Vatican Council. She worked in Rio de Janeiro and Bogotá for the USIA until 1964 and then moved to Caracas to write for Copley News Service, to which she remained bound by contract until 1967.