Just last Thursday, anti-secrecy group WikiLeaks, the recipient of materials from Manning, tweeted that its founder Julian Assange would agree to extradition if Manning was released.
Manning has been a focus of a worldwide debate on government secrecy since she provided more than 700,000 documents, videos, diplomatic cables and battlefield accounts - a leak for which she was sentenced to serve 35 years in prison.
Manning, formerly known as U.S. Army Private First Class Bradley Manning, was born male but revealed after being convicted of espionage that she identifies as a woman.
Manning, who is held at the Fort Leavenworth, Kansas, military prison, accepted responsibility for leaking the material. She has said she was confronting gender dysphoria at the time of the leaks while deployed in Iraq. Her sentence will now expire on May 17, the White House said.
Manning was working as an intelligence analyst in Baghdad in 2010 when she gave WikiLeaks a trove of diplomatic cables and battlefield accounts that included a 2007 gunsight video of a U.S. Apache helicopter firing at suspected insurgents in Iraq, killing a dozen people including two Reuters news staff.
Her attorney had argued her sentence exceeded international legal norms, and she has twice attempted suicide.
"If Obama grants Manning clemency Assange will agree to US extradition despite clear unconstitutionality of DoJ case," the WikiLeaks tweet of Jan. 12 said.
Assange has been holed up at Ecuador's London embassy since 2012 to avoid extradition to Sweden for the investigation of allegations, which he denies, that he committed rape in 2010.
Assange, who is Australian, says he fears further extradition from Sweden to the United States, where there is an open criminal investigation into the activities of WikiLeaks.
It also published emails in the weeks leading up to the Nov. 8 presidential election that U.S. intelligence agencies have concluded that Russian intelligence agencies hacked from the Democratic National Committee and the accounts of leading Democrats as part of a campaign to influence the election.
Obama also pardoned retired U.S. Marine Corps general James Cartwright who pleaded guilty in October to making false statements to the FBI during an investigation into leaks of classified information.
Manning was among 209 commutations granted by Obama on Tuesday and Cartwright was among 64 pardons.
Manning's clemency was criticized by Republican Senator Tom Cotton, who said Manning endangered troops, intelligence officers, diplomats and allies with the leaks.
"We ought not treat a traitor like a martyr," Cotton said.
But civil rights groups praised the move, calling it overdue.
"Chelsea Manning exposed serious abuses, and as a result her own human rights have been violated by the U.S. government for years," said Margaret Huang, executive director of Amnesty International USA.
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