His father served in the U.S. Marine Corps, and his brother was career military non-commissioned officer who retired at the rank of chief master sergeant in the U.S. Air Force.

Immediately after the attacks of September 11, 2001, he was assigned as the officer in charge of all West Coast SEAL Teams' training and readiness.

Lumpkin returned from Iraq for his final military assignment, working as a liaison to the U.S. Congress on policy and funding issues to support U.S. Special Operations Forces.

In 2010, Lumpkin began serving as both senior advisor to the secretary and deputy chief of staff for operations at the United States Department of Veterans Affairs.

In April 2011, Lumpkin moved over to The Pentagon, where he was sworn in as the Principal Deputy Assistant Secretary of Defense for Special Operations and Low-Intensity Conflict (SO/LIC).

He was also asked to lead DoD's response to the Ebola crisis in West Africa, and efforts to return Sergeant Bowe Bergdahl from the Taliban.

In January 2016, President Obama asked Lumpkin to overhaul the U.S. government's efforts to counter the propaganda of violent extremist organizations abroad such as the Islamic State in Iraq and the Levant.

He was appointed the special envoy and coordinator of the Global Engagement Center, an interagency organization that leverages the private sector and new data analytics tools to disrupt extremist violent propaganda.

His previous positions include director of business development at ATI, Chief Executive Officer at Industrial Security Alliance Partners, and Vice President for Human Performance at Leidos.