The Pentagon has named Paul Lewis as its special envoy for closing the US military prison at Guantanamo Bay, Cuba.
Defence Secretary Chuck Hagel announced the appointment on Tuesday.
It was part of President Barack Obama's renewed push to close the prison, which remains open despite his 2009 pledge to shutter the facility within a year.
Lewis has been an attorney for the Democratic minority on the House of Representatives Armed Services Committee, where he deals with Guantanamo-related issues.
"Special Envoy Lewis brings a wealth of experience from his previous position," the Pentagon said in a statement.
In his new position, he will work with the State Department on transferring Guantanamo detainees to other countries. He will also oversee efforts to transfer third-country nationals held by the US in Afghanistan.
He is to take up his position on November 1.
Obama created two special envoy positions to work on closing Guantanamo. Attorney Clifford Sloan was appointed in June to be the State Department envoy. Lewis will serve as his counterpart at the Pentagon.
Obama campaigned on a pledge to close the base, created under his Republican predecessor George W Bush to detain
prisoners held in the US fight against al-Qaeda following the September 11, 2001, attacks. But resistance in Congress and difficulty finding countries willing to take the inmates has prevented the closure.
There are currently 164 inmates held at the facility.