Marine Corps Gen James Mattis has been nominated to replace Gen David Petraeus as head of US Central Command.
The US Senate will have to confirm the nomination by Defence Secretary Robert Gates.
Central Command is responsible for overseeing the wars in Iraq and Afghanistan.
Gen Petraeus was confirmed last week as the US commander in Afghanistan, replacing sacked Gen Stanley McChrystal.
Gen McChrystal caused controversy after making derogatory remarks about senior civilian officials in a magazine article.
Gen Mattis, a counterinsurgency expert, led 2004's battle of Falluja in Iraq.
Speaking to reporters on Thursday, Mr Gates said: "The post General Mattis is taking is a critical one at a critical time".
He described Gen Mattis as one of the US military's "outstanding combat leaders and strategic thinkers".
He also praised the general's insight into the way the military must shape itself for the future.
