Byrne was Associate General Counsel and Chief Privacy Officer at Lockheed Martin. At Lockheed Martin, he also served as the company's primary cyber and counterintelligence attorney. Byrne served as a deployed Marine Infantry Officer. In 2004, he served active duty with the United States Marine Corps for 18 months, where he was an officer in charge of the Marine Liaison Office at medical centers in Maryland. In this capacity, he supported injured and deceased marines and their families. Byrne worked for the United States Department of Justice as an international narcotics prosecutor. He has also served as a career Senior Executive Service Deputy Special Counsel with the United States Office of Special Counsel and as both General Counsel and Assistant Inspector General for Investigations with the Special Inspector General for Iraq Reconstruction. He is a former adjunct professor of Marymount University and East Carolina University. Until August 2017, Byrne served on the U.S. Department of Homeland Security Data Privacy and Integrity Advisory Board and the International Association of Privacy ProfessionalsBoard of Directors. Byrne volunteers in his community, and has served on several non-profit and advisory boards. For ten years, he volunteered on the Executive Board of Give an Hour, a non-profit organization that has developed national networks of volunteer professionals capable of providing complimentary and confidential mental health services in response to both acute and chronic conditions that arise within our society, beginning with the mental health needs of post-9/11 veterans, service members and their families.
From 2017 to 2019, Byrne served as VA's General Counsel, being nominated by President Donald Trump. On August 28, 2018, Trump named Byrne as Acting Deputy Secretary of Veterans Affairs. On April 12, 2019, Trump nominated Byrne to serve permanently as Deputy Secretary of Veterans Affairs. He was confirmed by the Senate on September 11, 2019 and was sworn in on September 16, 2019. Byrne was fired from his position on February 3, 2020. The announcement of Byrne's firing said it was "due to loss of confidence" in his "ability to carry out his duties." Two days later Veterans Affairs Secretary Robert Wilkie described it as "a simple business decision".
