Janis Sharp said the treatment of her son, who admits hacking into military computers but claims he was looking for evidence of UFOs, was "barbaric".
This afternoon, she met supporters outside Number 10 to hand over poems of support for her son to mark the 10th anniversary of his first arrest.
She urged Prime Minister David Cameron to raise the issue with US president Barack Obama when the two leaders meet at the White House next month.
Ms Sharp said: "Ten years have gone by and still Gary lives in a nightmare world - unable to control the terror that consumes his every waking moment.
"This endless pressure on an Aspergic man with severe mental health issues is barbaric.
"And for what? A foolish act that caused embarrassment to the US. Where has our sense of proportion gone?"
She told reporters on Downing Street: "He can't deal with it. He sits in the dark - it's ruined his life.
"His mental health has deteriorated and it's ruined our lives."
And Ms Sharp said her son does not have an outlet because he cannot use a computer.
The High Court expressed concern over how long McKinnon's case was taking to return to court last month, with two judges listing the case for July in a bid to speed matters up.
They acted after hearing that Home Secretary Theresa May is "considering afresh" whether Asperger's sufferer McKinnon should be extradited to the US to face trial for hacking into military computers in 2002.
She said: "In March David Cameron is visiting President Obama to discuss our 'special relationship'.
"What an opportunity for our PM to finally announce an end to Gary's 10-year ordeal.
"This act alone would prove that the 'special relationship' has true meaning and is one of mutual respect."
McKinnon's legal team hopes Mrs May will block extradition amid predictions he could be jailed for 60 years in America.
Medical evidence shows the 45-year-old was "suffering from a serious mental disorder and there is a serious risk of suicide if extradited", his legal team has said.
McKinnon, from Wood Green, north London, admits hacking but claims he was looking for evidence of UFOs.
Arrested in 2002, and then again in 2005, 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".
An independent review of the UK's extradition arrangements by Sir Scott Baker last year found the current treaty between the US and the UK was both balanced and fair.
But the Government is under pressure to ignore its findings after MPs called on ministers to bring forward new laws and attempt to change the UK-US extradition treaty.
In a House of Commons debate in December, Tory MP Dominic Raab said: "Gary McKinnon should not be treated like some gangland mobster or al Qaida mastermind."
A number of other figures in high-profile cases are also fighting extradition to the US, including 23-year-old student Richard O'Dwyer who is accused of breaking American copyright laws.
Retired businessman Christopher Tappin, who is accused of conspiring to sell components for Iranian missiles, and Babar Ahmad, who is wanted for allegedly raising funds for Chechen and Afghan insurgents over the internet, are also fighting against extradition.
Ms Sharp added: "My heart goes out to others in a similar situation including Chris Tappin, Richard O'Dwyer and Babar Ahmad and their families, who are themselves suffering at the hands of a discredited piece of legislation.
"I remain confident our Government will eventually do the right thing and amend our extradition laws."
Shami Chakrabarti, director of the civil rights group Liberty, was also at Downing Street.
She said: "As Gary's ordeal continues so does the current rotten extradition regime.
"No-one is immune from unfair treatment and the lack of compassion in the system is already devastating too many lives.
"Liberty urges Government to honour the promises of opposition and put a little common sense and justice back into our extradition laws."
PA
