"The Department of Defense announced today the repatriation of Faez Mohammed Ahmed Al-Kandari from the detention facility at Guantanamo Bay to the government of the state of Kuwait," the Pentagon said in a statement.
The US military and intelligence agencies had "determined continued law of war detention of Al-Kandari does not remain necessary to protect against a continuing significant threat to the security of the United States."
According to his leaked prison file, published by the New York Times, 40-year-old Al-Kandari was a "committed member" of Al-Qaeda and was an influential religious figure for the group's fighters in Afghanistan.
President Barack Obama pledged to shut Guantanamo when he took office in 2009, but his efforts have been repeatedly thwarted by Congress.
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US Defense Secretary Ashton Carter last month approved the transfer of 17 low-risk detainees from Guantanamo, and two of these were released Wednesday.
Since 2002, a total of 779 detainees have been held at Guantanamo in connection with America's "war on terror."
Inmates are kept without recourse to regular US legal processes and some likely will die in prison without ever being convicted of a crime.