Karl credits his passion for history and journalism to a time in his adolescent years when his family moved to South Dakota. Karl graduated Phi Beta Kappa from Vassar College, Poughkeepsie, New York, in 1990, where he was the Editor-in-Chief of the Vassar Spectator.

Karl began his career as a researcher and reporter for The New Republic, continued as an investigative reporter for the New York Post, and became a Congressional Correspondent for CNN before joining ABC News in January 2003 as the Senior Foreign Affairs Correspondent covering the State Department. He worked for ABC covering national political news, becoming the Senior National Security Correspondent in December 2005. His current post is Chief White House Correspondent as of December 2012.

Karl received the 2011 Joan Shorenstein Barone Award for excellence in Washington, D.C.-based reporting, the 2013 Walter Cronkite Award for National Individual Achievement, an Emmy Award in 2009 for his coverage of the Presidential Inauguration of Barack Obama, and the National Press Foundation’s Everett McKinley Dirksen Award in 2001.

Karl became a controversial figure in May 2013, when he wrote an article that claimed to quote directly from an e-mail sent by a White House advisor. It was later revealed that the quote was inaccurately given to Karl by an unnamed source, and that he himself had never seen the e-mail. Karl apologized for the error, and also for not having stated that the quote was from a detailed summary his source provided, rather than a direct quote from the e-mail.