Following in the footsteps of his parents, he became a diplomat in 1965 and served in London, Paris (as ambassador), and other capitals. In 1978 he resigned as ambassador to France in protest over the appointment of Gustavo Diaz Ordaz, former president of Mexico, as ambassador to Spain. He has also taught courses at Brown, Princeton, Harvard, the University of Pennsylvania, Columbia, Cambridge, and George Mason University. He was a teacher at Brown University. He was also a friend of the U.S. sociologist C. Wright Mills, to whom he dedicated his book The Death of Artemio Cruz.
Fuentes fathered three children. Only one of them survived: Cecilia Fuentes Macedo, born in 1962, now working in television production. A son, Carlos Fuentes Lemus, died from complications associated with hemophilia in 1999 at the age of 25. A daughter, Natasha Fuentes Lemus (born 31 August 1974), died of an apparent drug overdose in Mexico City 22 August 2005, at the age of 30.
Carlos Fuentes received the Four Freedoms Award for Freedom of Speech and Expression in 2006, in Middelburg, the Netherlands.
On May 15, 2012, Consuelo Saizar, the head of the National Council for Culture and Arts, publicly announced the death of Carlos Fuentes at the age of 83. He died in a private hospital in southern Mexico City.
The author described himself as a pre-modern writer, using only pens, ink and paper. He asked, "Do words need anything else?" Fuentes mentioned that he detests those authors who from the beginning claim to have a recipe for success. In a speech on his writing process he mentioned that when he starts the writing process he begins by asking, "Who am I writing for?"
He published Las Buenas Conciencias in 1959. This is probably his most accessible novel depicting the privileged middle classes of a medium-sized town, probably modelled on Guanajuato.
His 1960s novels, Aura (1962) and La muerte de Artemio Cruz (1962) are acclaimed for using experimental modern narrative styles (including the second person form) to discuss history, society and identity.
In 1967, during a meeting with Alejo Carpentier, Julio Cortázar and Miguel Otero Silva, Carlos Fuentes launched the project of a series of biographies depicting Latin American caudillos, which would be called Los Padres de la Patria. Although the project was never completed, it provided the base for Alejo Carpentier's Reasons of State (El recurso del método, 1974) and various other Dictator Novels (novelas del dictador).
1975's Terra Nostra won the Venezuelan Rómulo Gallegos Prize.
His 1985 novel Gringo viejo, the first United States bestseller written by a Mexican author, was filmed as Old Gringo (1989) starring Gregory Peck and Jane Fonda.
In 1994, he published Diana, The Goddess Who Hunts Alone, a fictionalized account of his alleged affair with Jean Seberg. However, his account has been questioned several times.
Fuentes regularly contributed essays on politics and culture to the Spanish newspaper El País and the Mexican Reforma. He was an observer of Mexico-U.S. relations and critic of the United States' policies in Latin America. He also wrote Las Dos Elenas.