Theresa May vetoed the extradition of Gary McKinnon to the US today, in a move which could stoke tension in the special relationship.
The home secretary also introduced important changes to the extradition treaty, which many critics say is unbalanced in the US' favour.
"After careful consideration of all relevant material I've concluded Gary McKinnon's extradition would give rise to such a high risk of him ending his life that a decision to extradite would be incompatible with his human rights," May told the Commons.
May also announced plans for legislation to provide a 'forum' bar, where a court hearing establishes whether a suspect should stand trial.
The move would see prosecutors justify attempts at extradition in open court, ridding the current process of its lack of transparency and putting the final decision in the hands of a judge rather than a politician.
"It's us all together. We've done it," a clearly emotional Janice Sharp said of her son's campaign at a press conference later.
"We've won for the little person. Not just for the elite, for the little person."
Describing how Gary recieved the news, she said: "He literally couldn’t speak. And then he was hugging, and we cried. It’s so emotional.
"He said he felt like a dead person. He had no job, he had no children, he doesn’t go on holiday. He doesn’t leave the house. He felt he was worthless."
Back in the Commons, David Burrowes, McKinnon's local MP, thanked May for "saving my constituent's life".
He added: "Today is a victory for compassion. British principles of justice and fair play must return to extradition."
Dennis Skinner praised Janice Sharp, McKinnon's mother, who resides in his constituency.
"Without Janice sharp I doubt this decision could have been made," he said.
"I want to thank her for that Bolsover fighting spirit. When she gets on that television she rarely misses a chance."
The Islamic Human Rights Commission commented: "The facts are clear, Muslims are extradited, non-Muslims are not. Muslims face detention without charge, non-Muslims do not.
"In light of government actions it is clear that Muslims are seen as second class citizens in Britain."
The McKinnon decision will be a massive relief for the Asperger sufferer and his mother Janice, who has campaigned alongside him since he was arrested in 2002 for allegedly hacking into Pentagon computers from his London bedroom.
McKinnon said he was looking for evidence of UFOs and that the messages he left mocking their security measures were merely mischievous – but the US government took on a highly draconian approach to the matter and suggested he could be jailed as a terrorist threat for 60 years.
The family were elated when the coalition came to power, because Nick Clegg and David Cameron had been such stalwart allies in opposition. But in the two and half years since, they had little indication of his fate.
May started the review of the medical evidence once she came to office and the decision prompted a pause into the judicial review of previous home secretary Alan Johnson, who decided to extradite.
Johnson was unrepentant today, saying "the home secretary has made a decision today in her own party's best interests – not in the interest of the country."
The process was later lengthened again when McKinnon's team disputed the medical experts the Home Office planned to use.
The psychiatrists' study allowed May to block the extradition under both the Human Rights Act and the Extradition Act.
The Crown Prosecution Service (CPS) has already ruled out bringing charges against McKinnon.
The decision to change the legal arrangements around extradition reflects the recommendations of Scott Baker's review of the treaty.
While Baker found the provisions were not lop-sided he did recommend removing the home secretary's responsibility for the extradition arrangements and handing it to the judiciary.
May accepted the review's conclusion that the standards of 'probable cause' and 'reasonable suspicion' were roughly equivalent.
She rejected arguments for the use of prima facie evidence tests before extradition, saying it would be "absurd" to demand it of "mature legal systems" in the US, Canada and Australia when it is not required for other countries.