Aamer, originally from Saudi Arabia, has been detained at Guantanamo Bay in Cuba for more than 13 years without charge.
Shaker Aamer, the last remaining British resident in Guantanamo Bay prison, has been released.
Until Friday’s announcement of his release, Shaker had been held at the US detention facility for more than 13 years. He had never been charged and never tried.
Philip Hammond, British foreign secretary, said Aamer, 46, had left the US military base.
|Inside Story: Guantanamo – will it ever close?|
Aamer, a Saudi national, was arrested in Afghanistan in 2001. His family says he was doing charity work and that he was sold for a bounty to US forces.
US authorities alleged he was leading a unit of Taliban fighters.
His supporters have maintained he is an innocent man. They say he was held in appalling conditions at Guantanamo, sometimes in solitary confinement and beaten.
The US-run prison in Cuba, marred by numerous allegations of human-rights abuses, still holds 113 inmates.
A Mauritanian citizen held there for 13 years despite never being accused of a crime and being cleared for release years ago by the US government has finally been repatriated to his home country, the Pentagon said on Thursday.