Mattingly joined CNN in December 2015 as a New York-based correspondent and spent 2016 on the campaign trail covering Republican presidential candidates Chris Christie, John Kasich and Donald Trump, which included a series of investigative pieces into Trump's business history, finances and taxes. 
Previously, Mattingly worked at Bloomberg Television in Washington, where he served most recently as a national political correspondent and before that, as the network's White House correspondent. In that capacity, Mattingly covered all of the major presidential candidates and reported on the domestic and foreign policy actions of the Obama administration. 
He secured the first interview with then-Attorney General Eric Holder in the wake of the Edward Snowden revelations and throughout his tenure landed a series of exclusive interviews with top cabinet, administration and congressional officials. 
While covering the White House, Mattingly broke news on several elements of the administration's foreign, economic and legal policy and was a finalist for the Scripps Howard Distinguished Service to the First Amendment award for an investigation into the Obama administration's crackdown on government whistle-blowers.