John Francis Kelly was born on May 11, 1950, in Boston, Massachusetts. He joined the United States Marine Corps in 1970 but was later relieved of his duties in 1972 to go to college, as an inactive sergeant in the reserves. He resumed his service in the Marines in 1975 and initiated as a second lieutenant. In 1976, he graduated from the University of Massachusetts.

Kelly had a long career in the US Marines. He served at Headquarters Marine Corps in Washington, DC, as a Captain from 1981 to 1984. Kelly attended the Georgetown School of Foreign Service in 1984, earning his Master of Arts in National Security. He continued climbing the military ranks, becoming Major in 1987 at the Second Marine Division. He received his Master of Science in Strategic Studies from the National Defense University in 1995. Kelly was deployed in Iraq in 2002 and was promoted to Marine Corps Colonel.

After being nominated in January 2007, Kelly was confirmed by the Senate as a major general. Four years later, he became lieutenant general. He served as the senior military assistant to two secretaries of Defense. From 2012 to 2016, Kelly was commander of the United States Southern Command (SOUTHCOM) as a four-star general.

President Donald Trump chose Kelly as Secretary of Homeland Security, and the US Senate confirmed him by an 88 to 11 vote. He was sworn in on January 20, 2017. He only served briefly as Homeland Security Secretary, resigning in July 2017 to become White House Chief of Staff for President Trump. He served in that position until January 2019, when he was succeeded by Mick Mulvaney.