Kaplan was born in New York City in 1970. He graduated from Columbia University in 1993 with a degree in history. After graduation, Kaplan worked as a researcher for The New Republic. In 1995, he moved to the Middle East to work as a freelancer for The Wall Street Journal.
Kaplan covered the Iraq War and the War in Afghanistan for The New Republic and The Atlantic Monthly. He was also a regular contributor to The New York Times Magazine and The Washington Post. In 2004, Kaplan was awarded the Overseas Press Club Award for Best Reporting in Print for his coverage of the Iraq War.
Kaplan's first book, The Accidental Terrorist, was published in 2005. The book tells the story of a young Pakistani-American man who is recruited by al-Qaeda and sent to fight in Afghanistan. The Accidental Terrorist was a New York Times bestseller and was translated into more than a dozen languages.
Kaplan's second book, The Insurgents, was published in 2009. The book tells the story of the Iraqi insurgency against the American occupation. The Insurgents was also a New York Times bestseller and was translated into several languages.
In 2010, Kaplan was named a Nieman Fellow at Harvard University. He spent the year at Harvard studying the history of American foreign policy.
After leaving Harvard, Kaplan returned to journalism. He has written for The New Yorker, The New Republic, and The Atlantic. In 2014, Kaplan published his third book, Terrorist Hunter. The book tells the story of a CIA officer who is sent to Afghanistan to hunt down Osama bin Laden.
Kaplan is also an activist. He is a member of the ACLU and the Brennan Center for Justice. He has spoken out against the use of torture, warrantless surveillance, and indefinite detention.
Kaplan is married to Rebecca Frankel, a journalist. They have two children.