Updated May 18, 2017 00:22:31

Photo: Chelsea Manning's sentence was shortened by Barack Obama in one of his last acts as president. (Reuters: US Army)

Chelsea Manning has walked out of a US military prison, seven years after being arrested for passing secrets to WikiLeaks in the largest breach of classified information in US history.

Manning, 29, was released from the US Disciplinary Barracks at Fort Leavenworth, Kansas, at about 2:00am (local time), according to a brief statement released by the US Army.

The former military intelligence analyst, then known as Private First Class Bradley Manning, was convicted of providing more than 700,000 documents, videos, diplomatic cables and battlefield accounts to WikiLeaks, an international organisation that publishes such information from anonymous sources.

The Oklahoma native was convicted in 2013 of 20 counts, including six espionage act violations, theft and computer fraud.

WikiLeaks founder Julian Assange, a target of criminal investigations in Sweden and the United States, has promised to accept extradition if Manning was freed.

US Attorney-General Jeff Sessions has said Mr Assange's arrest was a priority.

Manning said in 2014 that she chose to disclose the classified information to expose truths about the civil war in Iraq "out of a love for my country".

Before he left office, former president Barack Obama commuted the final 28 years of Manning's 35-year sentence.

The decision angered national security experts who say Manning put US lives at risk, but it won praise from transgender advocates who have embraced her transition to a female gender identity.

In a statement to ABC News (America), Manning said she appreciated the support she had received from people all over the world.

"As I rebuild my life, I remind myself not to relive the past," the statement said.

"The past will always affect me, and I will keep that in mind while remembering that how it played out is only my starting point — not my final destination."

WikiLeaks began revealing secrets in 2007 and then burst onto the wider public consciousness three years later with a series of releases, including material gathered by Manning during her stint as an intelligence analyst in Baghdad.

Among the material from her was a 2007 gunsight video of a US Apache helicopter firing at suspected insurgents in Iraq, killing a dozen people, including two Reuters news workers.

Manning thanks former president Barack Obama

In a statement last week — her first public comments since Mr Obama intervened — Manning thanked the former president and said letters of support from veterans and fellow transgender people inspired her "to work toward making life better for others".

Here's what we know about the woman responsible for the largest breach of classified information in America's history.

"For the first time, I can see a future for myself as Chelsea," she said.

"I can imagine surviving and living as the person who I am and can finally be in the outside world.

"Freedom used to be something that I dreamed of but never allowed myself to fully imagine."

Critics said Manning's leaks laid bare some of the country's most-sensitive secrets and endangered information sources, prompting the US State Department to help some of those people move to protect their safety.

Several ambassadors were recalled, expelled or reassigned because of embarrassing disclosures.

Manning's lawyers have said Manning was subjected to violence in prison and argued the military mistreated her by requiring her to serve her sentence in an all-male prison, restricting her physical and mental health care and not allowing her to keep a feminine haircut.

The Army said on Tuesday that Manning would remain on active duty in a special, unpaid status that will legally entitle her to military medical care, along with commissary privileges.

An Army spokeswoman, Lieutenant Colonel Jennifer Johnson, said Manning will be on "excess leave" while her court-martial conviction is under appellate review.

Reuters/AP

Topics: prisons-and-punishment, law-crime-and-justice, government-and-politics, security-intelligence, defence-and-national-security, united-states

First posted May 17, 2017 22:28:24