British terror suspect Babar Ahmad pleaded guilty to two counts of providing support to terrorists, in US District Court in New Haven, Connecticut.
He did not plead guilty to two additional charges that also included conspiracy to injure the property of a foreign government and money laundering.
US prosecutors said that Ahmad and another man, Syed Talha Ahsan, ran a website that raised funds for Muslim militants in Afghanistan and Chechnya.
The two were extradited to the US from Britain last year.
Ahmad faces the possibility of up to 25 years in prison and two to five years' probation.
British terror suspect Babar Ahmad has pleaded guilty in the US to two offences relating to supporting terrorism.
The computer expert from Tooting, south London, admitted operating a website that promoted jihad and supported al Qaeda. But he denied two other charges.
He was extradited from the UK last year.
The family of terror suspect Babar Ahmad, who was extradited alongside radical cleric Abu Hamza earlier this month, has accused the Government of "blatant old-fashioned racism".
Ahmad's family said in a statement that today's decision to block Gary McKinnon's extradition is "a clear demonstration of double standards".
"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."