Guillermoprieto was born and grew up in Mexico City. In her teens, she moved to New York City with her mother where she studied modern dance for several years. From 1962 until 1973, she was a professional dancer.
In the mid-1970s, she started her career as a journalist for the Guardian, moving later to the Washington Post. In January, 1982, Guillermoprieto, then based in Mexico City, was one of two journalists (the other was Raymond Bonner of The New York Times) who broke the story of the El Mozote massacre in which some 900 villagers at El Mozote, El Salvador, were slaughtered by the Salvadoran army in December, 1991. With great hardship and at great personal risk, she was smuggled by FMLN rebels to visit the site approximately a month after the massacre took place. When the story broke simultaneously in the Post and Times on January 27, 1982, it was dismissed as propaganda by the Reagan administration, as it seriously undermined efforts by the US government to bolster the human rights image of the Salvadoran government, which the US was supporting with large amounts of military aid. Subsequently, however, the details of the massacre as first reported by Guillermoprieto and Bonner were verified, with widespread repercussions.
During much of the subsequent decade, Guillermoprieto was a South America bureau chief for Newsweek.
Her first book, Samba (1990), was an account of a season studying at a samba school in Rio de Janeiro.
During the 1990s, she came into her own as a freelance writer, producing long, extensively researched articles on Latin American culture and politics for The New Yorker and The New York Review of Books, including outstanding pieces on the Colombian civil war, the Shining Path rebel movement in Peru, the aftermath of the "Dirty War" in Argentina, and post-Sandinista Nicaragua. These were bundled in the book The Heart That Bleeds (1994), now considered a classical portrait of the politics and culture of Latin America during the "lost decade" (it was published in Spanish as Al pie de un volcán te escribo — Crónicas latinoamericanas in 1995).
In April 1995, at the request of Gabriel García Márquez, Guillermoprieto taught the inaugural workshop at the Fundación para un Nuevo Periodismo Iberoamericano, an institute for promoting journalism that was established by García Márquez in Cartagena de Indias, Colombia. She has since held seven workshops for young journalists throughtout the continent.
That same year, Guillermoprieto also received a MacArthur Fellowship.
A second anthology of articles, Looking for History, was published in 2001. Guillermoprieto also published a collection of articles in Spanish on the Mexican crisis, El año en que no fuimos felices.
As of 2003, Guillermoprieto is working on a memoir, an excerpt of which was published earlier in the year in The New Yorker. The book is due to be published in February, 2004.