In 1998, shortly after receiving a master's degree from Oxford University, Mazzetti began reporting on national politics as a correspondent for The Economist.

In 2004 Mazzetti joined the staff of the Los Angeles Times, and continued working with the Pentagon as a military affairs correspondent.

In late 2007, he broke the story of the CIA's destruction of interrogation video tapes depicting torture of Al Qaeda detainees.

In addition to sharing the Pulitzer Prize for International Reporting in 2009, he won the George Polk award with colleague Dexter Filkins for coverage of the secret wars being waged in Pakistan and Afghanistan.

[citation needed] In May 2011, Charles Kaiser cited a story written by Mazzetti in collaboration with Helene Cooper and Peter Baker "which credulously adopted the line of former Bush administration officials who were desperately trying to convince the world that torture was the main reason that Bin Laden had been located.

[8] The article exposed how mercenaries hired by Erik Prince, the former head of Blackwater, training Somalis to combat piracy by the abandoned the program.

[9] In 2011, he furnished the pre-publication text of an opinion column written by Maureen Dowd concerning the making of the movie "Zero Dark Thirty" to CIA spokesperson Marie Harf for review.