Known for his blunt, hard-driving style, he served three tours in Iraq. His son, Marine Lt. Robert Kelly, was killed in November 2010 in Afghanistan.
Kelly has experience in Washington as a top military aide to two Defense secretaries, and as a Marine Corps liaison to Congress. He served as head of U.S. Southern Command before he retired.
The Pentagon command is responsible for U.S. military operations in Latin America and the Caribbean and works closely with the Department of Homeland Security to combat human trafficking and drug smuggling.
Lawmakers from both parties noted that Kelly's time at Southern Command prepared him for many of the same problems he would confront at Homeland Security.
Like Trump, Kelly made clear that he believed tougher measures were needed to interdict migrants crossing the southwest border from Mexico.
He recounted visiting the border with law enforcement officers recently and observing several people climb over a chain-link fence, part of the barriers that already exist along parts of the border.
He said the officers did not move to arrest the fence-jumpers.
"What's the use?" he said, describing the officers' attitude of the futility of holding back migrants. "That's not good for morale."
If confirmed, he said his priority would be to "let the people who are tasked with protecting the border do their job."
Border Patrol agents and other U.S. authorities apprehended 408,870 people on or near the border -- including 137,366 children and their families, mostly from Central America -- in the just-ended 2016 fiscal year, according to U.S. records.