He graduated from the United States Army's Ranger School, served in the first Gulf War and in peacekeeping operations during the Los Angeles riots in 1992 before being honorably discharged as a captain in 1994.

He was there on the morning of the September 11 attacks, and discreetly reported from Ground Zero for the Times for the next twelve days, parlaying his Marine identity and volunteering in order to remain after most of the press was cleared to facilitate rescue, recovery, and clean-up efforts.

[11][12][13] In 2013 Chivers published an article in The New York Times about the ordeal of photojournalist Matt Schrier as hostage in the hands of Syrian rebels while his cellmate journalist Peter Theo Curtis still was held captive.

[15] In 2015 Esquire magazine said Chivers was "the most important war correspondent of his time", saying he developed "a brand of journalism unique in the world for, among other things, its study of the weapons we use to kill one another".

The scope included the biographies of Hiram Maxim, Richard Gatlin, Paul Mauser, John T. Thompson, their eponymous automatic weapons, and their impact on warfare; the origin of the Soviet AK-47 rifle; and the contest between the AK-47 and the M16 in the Vietnam War, and the spread of the adoption of the AK-47 by criminal, non-military, non-state actors.

[24][16][25] Two of Chivers' stories from Afghanistan were included in The New York Times' submission to the 2002 Pulitzer Prize for Public Service, which was awarded to the team behind A Nation Challenged, "a special section published regularly after the September 11th terrorist attacks.

[28] With Steven Lee Myers, Chivers received a citation for best newspaper reporting from abroad from the Overseas Press Club for coverage of the 2004 Beslan school hostage crisis in The Times.

Through careful, persistent reporting, Chivers provided Esquire readers with a haunting look at how innocent hostages, Chechen terrorists, and Russian authorities responded to a crisis that left 362 dead."

[36] Chivers was the 2007 winner of the Jesse Laventhol Prize for Deadline Reporting, awarded by the American Society of Newspaper Editors for his account in The Times of a Navy corpsman's efforts to save a Marine wounded by a sniper in Al Anbar Governorate, Iraq.

[41] Chivers won the 2011 George Polk Awards in Journalism in the category of Military Reporting presented by Long Island University, citing his "courageous and illuminating coverage of the wars in Libya and Afghanistan" and his "weapons expertise".

[46][47] On November 29, 2012, Chivers delivered the 32nd Joe Alex Morris Jr. Memorial Lecture at the Nieman Foundation for Journalism at Harvard University, an invited talk on the topic of international reporting which honors an American overseas correspondent or commentator on foreign affairs.

The citation read "For showing, through an artful accumulation of fact and detail, that a Marine’s postwar descent into violence reflected neither the actions of a simple criminal nor a stereotypical case of PTSD (Posttraumatic stress disorder)."

His winning article, "The Fighter", in The New York Times Magazine tells the story of "a veteran infantry combat Marine who was struggling with adjusting to life after serving in the war in Afghanistan".