The mother of Gary McKinnon said she was "overwhelmed" when she learned he had won his 10-year battle against extradition to the US.
Janis Sharp was speaking after the Home Secretary stopped the self-confessed computer hacker being sent to the US to face trial due to fears for his health.
"It's been an emotional rollercoaster," Ms Sharp said.
"I'm overwhelmed. I'm incredibly happy. I want to say thank you (to) Theresa May, because it was an incredibly brave decision to stand up to another nation as strong and powerful as America.
"To also change the extradition treaty to bring in forum so that this hopefully happen to anyone else, is absolutely incredible.
"Without people power, of all these different people together, there's no way Gary would have stayed here. We've won for the little person."
She said Mr McKinnon, from North London, was also coming to terms with Mrs May's announcement.
"He's still incredibly emotional," she said. "He couldn't speak. He said that he (had) felt like a dead person. He felt he was worthless."
Addressing the Commons earlier, Mrs May had also announced a shake-up of existing extradition arrangements, introducing a forum bar which will allow a UK court to decide if a trial should be brought here instead.
Mr McKinnon, who suffers from Asperger's syndrome - a high-functioning form of autism - admits hacking into US military computers but claims he was looking for evidence of UFOs.
The 46-year-old could have faced up to 60 years in prison in America if convicted.
A spokeswoman for the US Justice Department said: "The United States is disappointed by the UK Home Secretary's decision not to extradite Gary McKinnon, particularly given the past decisions of the UK courts and prior Home Secretaries that he should face trial in the United States.
"We note that the Home Secretary has described this case as exceptional and, thus, this decision does not set a precedent for future cases."
Mrs May took the highly unusual step of blocking the application after Home Office medical evidence found Mr McKinnon was very likely to attempt suicide if he was extradited.
She told MPs: "Mr McKinnon is accused of serious crimes but there is also no doubt that he is seriously ill. He has Asperger's syndrome, and suffers from depressive illness.
"The legal question before me is now whether the extent of that illness is sufficient to preclude extradition.
"After careful consideration of all of the relevant material, I have concluded that Mr 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 Mr McKinnon's human rights.
"I have therefore withdrawn the extradition order against Mr McKinnon. It will now be for the Director of Public Prosecutions to decide whether Mr McKinnon has a case to answer in a UK court."
Shami Chakrabarti, director of civil rights group Liberty, commented: "This is a great day for rights, freedoms and justice in the United Kingdom.
"The Home Secretary has spared this vulnerable man the cruelty of being sent to the US and accepted Liberty's long-standing argument for change to our rotten extradition laws."
London mayor Boris Johnson added: "At last, justice and the well-being of Mr McKinnon have prevailed. To extradite a man diagnosed with Asperger syndrome to America for trial would have been extraordinarily cruel and inhumane. I applaud the Government's stance."
But the family of terror suspect Babar Ahmad, who was extradited alongside radical cleric Abu Hamza earlier this month, accused the Government of "double standards".
"Many of our supporters are angry at what appears to be blatant old-fashioned racism under which all British citizens are equal but some are more equal than others," his family said.
"We would not want his family to experience the pain and suffering we have all been enduring since Babar was extradited," they said.
"However, questions do need to be asked as to why within the space of two weeks, a British citizen with Asperger's accused of computer related activity is not extradited, while two other British citizens, one with Asperger's, engaged in computer related activity are extradited."
Ecuador drew parallels between Mr McKinnon's case and that of Wikileaks founder Julian Assange, who has been staying in their London embassy since June as he seeks to avoid extradition to Sweden.
An embassy spokesman said: "The UK government ought to now publicly state that they will not, under any circumstances, allow the onward extradition of Julian Assange to the US where he would be subject to the undermining of his human rights just as Gary McKinnon would have been."
Mr McKinnon was arrested in 2002 and then again in 2005 before an order for his extradition was made in July 2006 under the 2003 Extradition Act.
That triggered three successive applications for judicial review and questions about the fairness of the UK-US extradition treaty, which critics claim is "one-sided".
Prime Minister David Cameron and Deputy Prime Minister Nick Clegg had both publicly condemned plans to send Mr McKinnon to the US.