Gertz was born on Long Island, New York. He has taken classes at Washington College and George Washington University. He has also written for National Review, The Weekly Standard and Air Force Magazine. He has lectured on defense, national security, and media issues at the Defense Department’s National Security Leadership Program, Johns Hopkins University School of Advanced International Studies, the FBI National Academy, the National Defense University, and the CIA. He has been a media fellow at the Hoover Institution on War, Revolution and Peace at Stanford University. He lives in Maryland.

In 2008, Gertz was subpoenaed to the Santa Ana, California federal court to testify in the case of Chi Mak, who was convicted of providing United States Navy technology to China. Gertz refused to answer questions about his sources, citing the Fifth Amendment.

During 1996 Gertz reported in the Washington Times on Chinese sales of nuclear technology to Pakistan. In 1997 he reported on Russian aid to Iran's nuclear weapon program, based on information given him by the Israeli intelligence agency Mossad. In 1998 he reported on United States sale of missile technology to China. In 2004, Gertz claimed that Syria, possibly with the aid of Russian troops, transferred Iraqi weapons of mass destruction stockpiles to its own military installations.

Gertz's 2000 book, The China Threat: How the People's Republic Targets America, presented the case that China's military was more modern and powerful than was its reputation in the United States military and intelligence communities. His 2002 book, Breakdown: How America's Intelligence Failures Led to Sept. 11, examined the activities of United States intelligence agencies prior to the 2001 terrorist attacks. His 2004 book, Treachery: How America’s Friends and Foes Are Secretly Arming Our Enemies, accused United States allies, including France and Germany of helping to arm terrorists. His 2008 book, The Failure Factory: How Unelected Bureaucrats, Liberal Democrats, and Big Government Republicans Are Undermining America's Security and Leading Us to War, said that many federal bureaucrats hold liberal views on foreign policy.