Computer engineer Babar Ahmad was sentenced to twelve and a half years by a court in Connecticut last July after pleading guilty to conspiring to support and providing material support to the Taliban regime in Afghanistan.
Ahmad, 41, was extradited to the US in 2012 after being arrested in Britain in 2004. He spent ten years behind bars in Britain before his deportation, which counted towards his sentence.
"Eleven years of solitary confinement and isolation in 10 different prisons has been an experience too profound to sum up in a few words here and now," the British citizen said in a statement.
His relatives added: "We, the family of Babar Ahmad, are delighted to announce that by the grace of God Babar has returned home to us after 11 years in prison."
Campaigners say Ahmad, who was released last month, was the Briton held the longest without charge as part of the US-led "war on terror."
US prosecutors said he had used his website to recruit and arrange for would-be fighters to travel to Afghanistan to train, and to solicit military uniforms and gas masks for the Taliban.