A native of New Jersey, Reilly began his journalism career at his high school in Philadelphia, where he was threatened with expulsion for refusing to reveal his source on a story that the administration banned from being published. He continued to pursue reporting as a media studies major at Catholic University in Washington, where he served as editor of the student newspaper and was named one of the top 100 student journalists in the country in 2009.

During his time at Bloomberg, Reilly worked on a project about health care lobbying that was a finalist for the Scripps Howard Journalism Award for Washington reporting. He has also written for The Gazette (Md.), The Courier-Post (N.J.), The Washington Times, and Washington City Paper, where he worked as an intern.