Lee Jin-man/AP
"Barring any last minute complications, Ash Carter will be President Barack Obama's choice as the new Secretary of Defense," several US administration officials reportedly told CNN.
The selection comes after a number of front runners for the job took themselves out of consideration, including former Pentagon policy head Michele Flournoy and Rhode Island Senator Jack Reed.
Carter was "responsible for the day-to-day management" of the Defense Department's 2.2 million employees during his ten months at Deputy Secretary of Defense under Hagel, but resigned in October of 2013 - possibly because of his discomfort with being passed over for the Pentagon's top job at the beginning of Obama's second term.
Carter was influential in reorganizing US Cyber Command during his time at the Pentagon, and helped to push cyber-security as a national security priority.
Hagel was reportedly forced to resign on November 24th, reportedly over disagreements with the White House over its handing of the US-led campaign against ISIS, along with more general policy disagreements over the US approach to the conflicts in Iraq and Syria.
"We have no Presidential personnel announcements at this time, and not going to speculate on any before the President announces it," White House Deputy Press Secretary Eric Schultz told Business Insider.