A spokesperson for the president-elect said no official decision has been made, although Mattis has been favourite for the job since Trump's election.
US president-elect Donald Trump has named James Mattis to head up the Pentagon as Secretary of Defense, less than four years after the former Marine General hung up his uniform.
However, if Mattis – known as “Mad Dog” is to take the job Congress will need to pass legislation allowing him to do so because a federal law states that defense secretaries must not have been on active duty for at least seven years before taking the role.
An exception has only been granted once before, when General George C. Marshal was appointed in 1950.
— viral (@VirAlThENEWS) 2 December 2016
Mattis, who has previously said that “beer and cigarettes” work better than waterboarding in terror suspect interrogations, has been the frontrunner for the job since Trump was elected.
Since retiring as the chief of U.S. Central Command in early 2013 after more than four decades in the Marine Corps, the 66-year-old has served as a consultant and as a visiting fellow at the Stanford University think tank, the Hoover Institution.
He is known as an influential leader and a strategic thinker but his aggressive talk has previously drawn criticism.
Like the president-elect, he is known to harbour strong opinions on foreign powers.
Speaking at the Center for Strategic and International Studies in April 2016, the retired general said he understood the need to combat extremist groups such as ISIL and al-Qaeda, but that the Iranian regime is “the single most enduring threat to stability and peace in the Middle East.”