In addition to having four decades of military experience, the 66-year-old four-star general is also the highest-ranking military officer to ever have a child killed in combat in Afghanistan or Iraq. His son, Robert Michael Kelly, died after stepping on a land mine in Afghanistan in 2010.
According to Trump's transition team, that experience played a key role in Trump's selection of Kelly. The president-elect reportedly wanted the person defending America from terrorism to personally understand the costs of war.
Kelly's qualifications for the job also stem from his time as the head of the United States Southern Command from 2012 to 2016, which helps take a more humanitarian approach to the countries it works with in the Caribbean and Central and South America. According to Politico, that position has readied him to oversee Trump's controversial immigration agenda at the US-Mexico border.
Kelly's role with the Southern Command also gave him insight into how the United States treats suspected terrorists, specifically at Guantánamo Bay. He's been an outspoken critic against closing the prison and has defended the often-criticized treatment of detainees, including force-feeding those who choose not to eat.
Trump will most likely make the selection official in an announcement next week.
Watch: National Security and Silicon Valley