"Today was a victory of sorts for Edward Snowden and his many supporters," Assange said in the statement, which was posted on the WikiLeaks website on Saturday.
"As Snowden has stated, his biggest concern was if he blew the whistle and change did not occur. Well reforms are taking shape, and for that, the President and people of the United States and around the world owe Edward Snowden a debt of gratitude."
Assange, who has been holed up at the Ecuadorean Embassy in London for more than a year, fearing extradition to the United States for publishing classified US documents, rejected Obama's assertion that his reforms were planned before Snowden's disclosures about US surveillance activities.
"The simple fact is that without Snowden's disclosures, no one would know about the programs and no reforms could take place," he said.
Assange accused the US government of "stunning" hypocrisy in its treatment of Snowden while it gave asylum to thousands of dissidents, whistleblowers and political refugees from countries like Russia and Venezuela.
The Obama administration has vigorously pursued Snowden to bring him back to the United States to face espionage charges for leaking details of US surveillance programs to the media. Snowden is now in Russia, where he has been granted asylum.
Assange himself is wanted in Sweden on sexual abuse allegations he denies. He has sought sanctuary in the Ecuadorean Embassy in London because he fears he could be extradited to the United States to face potential charges over the release of thousands of confidential US documents on WikiLeaks.
Assange charged that the Obama administration had prosecuted "twice as many" whistleblowers as all other US administrations combined, in spite of the president's 2008 campaign pledge to champion transparency and those who fought for it.
He said it was fortunate for the world that Snowden and others "of good conscience," like Private First Class Bradley Manning - who was convicted last month of leaking classified data to WikiLeaks - had chosen not to remain silent.
In announcing his reform plans on Friday, Obama vowed to improve oversight of surveillance and restore public trust in the government's programs, saying the United States "can and must be more transparent."