The President also pardoned James Cartwright, the former vice chairman of the US Joint Chiefs of Staff, who pleaded guilty in October to a single charge of making false statements to federal investigators in 2012 when he was questioned about leaking top secret information on US efforts to cripple Iran's nuclear program to two journalists.
Manning, a transgender woman and former US Army soldier, was serving a 35-year sentence at Fort Leavenworth, an all-male Army prison in eastern Kansas, despite her request to transfer to a civilian prison. A White House statement on Tuesday said her prison sentence is set to expire on May 17.
The material, which WikiLeaks published in 2010, included a classified video of a US helicopter attacking civilians and journalists in Iraq in 2007. Labeled "Collateral Murder," the film drew criticism from human rights activists for the deaths of innocent people.
When asked about WikiLeaks in the wake of the releases, President-elect Donald Trump told Fox News' Brian Kilmeade in 2010: "I think it's disgraceful. I think there should be like death penalty or something."
Though found guilty on 20 out of 22 possible charges (including violating the US Espionage Act), Manning was not convicted of the most serious one; aiding the enemy, which could have earned the private a life sentence.
Instead, the former intelligence analyst was sentenced to 35 years in prison, as well as demoted from private first class to private and dishonorably discharged.
A former intelligence official described being "shocked" to learn of Obama's decision Tuesday. The official added that the "entire intelligence community is deflated by this inexplicable use of executive power," saying it was "deeply hypocritical given Obama's denunciation of WikiLeaks' role in the hacking of the (Democratic National Committee)."
WikiLeaks declares 'victory'
Earlier this month, WikiLeaks said it would agree to a US extradition request for the site's founder, Julian Assange, if Obama granted clemency to Manning. It was not immediately clear if WikiLeaks would make good on its promise, though the group declared "victory" in a tweet Tuesday afternoon.
Meanwhile, Edward Snowden, the former National Security Agency contractor who leaked state secrets in 2013 and is living in exile in Russia,
tweeted his support of Manning, urging her to "stay strong a while longer."
Chase Strangio, an attorney for the American Civil Liberties Union, which represented Manning, said he was "relieved and thankful" Obama commuted her sentence, and Amnesty International also cheered news of Manning's commutation.
"Chelsea Manning exposed serious abuses, and as a result, her own human rights have been violated by the US government for years," Margaret Huang, the group's executive director, said in a statement. "President Obama was right to commute her sentence, but it is long overdue. It is unconscionable that she languished in prison for years while those allegedly implicated by the information she revealed still haven't been brought to justice."
Republican members of Congress, however, expressed outrage.
"This was grave harm to our national security. and Chelsea Manning is serving a sentence and should continue to serve that sentence," Sen. Tom Cotton, R-Arkansas, told CNN's Jake Tapper on "The Lead."
Meanwhile, Sen. Bill Cassidy, R-Louisiana, told reporters on Capitol Hill that he considered Manning a "traitor" and said he was "disappointed" about the commutation.
"If somebody leaks our state secrets, endangers Americans directly, we need to set an example that is severe and consistent," he said.
Two-year sentence sought for Cartwright
Cartwright's career was marked by decades of distinguished military service. From August 2007 to August 2011, he served as the second-highest uniformed officer and, before that, he served as commander of US Strategic Command. During his tenure in these posts, he held the highest security clearance, and retained top security clearance upon his retirement from the military in 2011.
"We are deeply grateful for President Obama's decision to pardon General Cartwright. ... Current and former leaders of the American national security community have, almost with one voice, stood up for General Cartwright. We thank them for supporting a man who is truly one of our nation's heroes," Cartwright's attorney and former White House counsel, Gregory Craig, said in a statement.
Federal prosecutors had sought a two-year prison sentence for Cartwright in court filings earlier this month, but his attorneys asked for probation, emphasizing his desire to persuade journalists to modify their reporting to protect national security interests.
"General Cartwright understands the magnitude of his offense and deeply regrets the decision that he made ... He has accepted responsibility and acknowledged his guilt," his attorneys wrote in court papers.
"(I)n General Cartwright's communications with both journalists, he successfully persuaded them not to report information that would be harmful to the United States."
One of those reporters, David Sanger of The New York Times, submitted a letter in support of Cartwright explaining that "throughout the interview, (Cartwright) consistently showed his concern that information damaging to US interests not be made public."
The other reporter, Daniel Klaidman, who wrote for Newsweek, also submitted a letter on Cartwright's behalf, as did several current and former members of Congress, along with military officials from the Bush and Obama administrations, all urging the judge for leniency in light of Cartwright's decorated military career.
Cartwright, 67, served 40 years in the US Marine Corps and was widely regarded within the military for his technical acumen and work in the areas of nuclear proliferation, missile defense and cybersecurity.
He was scheduled for sentencing before DC District Court Judge Richard Leon on January 31.
