Chelsea Manning will be released from a military prison in Kansas on May 17 this year, after President Barack Obama commuted her sentence in his last week in office.

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

What's her background?

Chelsea Manning, formerly Bradley Manning, was born in Oklahoma in 1987, and was raised in the small town of Crescent.

She moved to Wales after her parents divorced when she was a teenager, and went on to join the US Army in 2007 after she finished high school.

What did she reveal?

In 2009, Manning was sent to Iraq as an intelligence analyst. That's where she gained access to the sensitive military files that she would soon send to WikiLeaks.

The video showed an American air strike in Baghdad. ( Youtube: sunshinepress )

More than 700,000 documents, videos and diplomatic cables were sent to the anti-secrecy group which then went on to publish many of them, including via news outlets The Guardian and The New York Times.

The leaks dominated the news agenda, with journalists scouring the files for what they revealed about the Iraq and Afghan wars.

One of the major leaks was a classified video which WikiLeaks called "Collateral Murder", which showed an airstrike in Baghdad on July 12, 2007.

The attack on suspected Iraqi insurgents killed a dozen people, including a news photographer and his assistant. A US military spokesman said a camera had been mistaken for a grenade launcher.

Another video showed a US air strike on an Afghan village which killed 100 civilians in May 2009.

When was she convicted?

Manning was arrested in May 2010 and went on trial in June 2013.

Chelsea Manning was sentenced to 35 years' jail. ( Reuters: US Army )

She had been charged with 22 offences, of which she pleaded guilty to 10 counts, including misusing classified material.

Military judge Colonel Denise Lind found Manning guilty of 20 of the charges, but she was acquitted of aiding the enemy.

During the trial, evidence against Manning included chat logs from a personal computer, admissions and a familiarity with WikiLeaks founder Julian Assange.

In August 2013, Manning was handed a 35-year sentence, with the chance of parole after seven years.

Manning was also dishonourably discharged from the Army and reduced in rank from private first class to private, the lowest rank in the military.

Did the penalty match the crime?

The sentence was the longest ever given in a case involving a leak of US government information for the purpose of it being reported to the public.

But it was less than the 60-year-sentence called for by the prosecution.

At the time, Manning's lawyer David Coombs said they would be applying for a presidential pardon.

Other cases involving whistleblowers, including former Navy intelligence officer Samuel Morison, show just how large the sentence was.

Morison was sentenced to two years for giving classified satellite surveillance photographs to Jane's Defense Weekly in 1985.

He was later pardoned by president Bill Clinton in 2001.

When did Manning become Chelsea?

Following her conviction, Manning revealed that she identified as a woman, and changed her name from Bradley to Chelsea.

Last year, she was allowed by the army to receive gender transition surgery.

Were there calls for her release?

Yes, several.

Many protests have been held before, during and after Manning's trial and organisations like Amnesty International even called on the US Government for her to be released.

Those calls intensified after Manning tried to take her own life in July and October last year.

The campaign #HugsForChelsea called on President Barack Obama to give Manning clemency.

Social media users on Twitter, Facebook and Instagram took photos of themselves with their arms out or with a #HugsForChelsea sign.

Campaign organisers also asked those not on social media to call the Office of the Pardon Attorney.