US soldier Bradley Manning has been found not guilty of aiding the enemy for giving troves of US government secrets to WikiLeaks, but guilty of other charges including theft and espionage.

The military judge hearing the court-martial for the former intelligence analyst announced her decision at 3am AEST.

Judge Colonel Denise Lind deliberated for about 16 hours over three days before reaching her decision in a case that drew worldwide attention as supporters hailed Manning as a whistleblower. The US government called him an anarchist computer hacker and attention-seeking traitor.

Who is Bradley Manning and why should you care?

Manning faced 21 counts including espionage, computer fraud and theft charges. He was convicted of five espionage counts, five theft charges, a computer fraud charge and other military infractions.

However, he was found not guilty on the most serious charge of aiding the enemy, which carried a possible life sentence without parole. He was also acquitted of one other charge.

What did Bradley Manning actually leak?

Manning, a 25-year-old native of Crescent, Oklahoma, has admitted to sending more than 470,000 Iraq and Afghanistan battlefield reports, 250,000 US State Department diplomatic cables and other material, including several battlefield video clips, to WikiLeaks while in Iraq in early 2010. WikiLeaks published most of the material online.

A video, titled "Collateral Murder", was released by Manning in 2010 and included footage of a 2007 US Apache helicopter attack in Baghdad that killed at least nine men, including a Reuters news photographer and his driver.

Manning's lawyers painted him as a naive young soldier, struggling with gender identity disorder and troubled by US actions in Iraq.

Wikileaks 'traitor' wanted to be born a woman

Manning stood and faced the judge as she read the decision. She didn't explain her verdict, but said she would release detailed written findings. She didn't say when she would do that.

Manning's attorney, David Coombs, smiled faintly when he heard not guilty on aiding the enemy, which carried a potential life sentence.

Assange calls convictions 'national security extremism'

When the judge was done, Mr Coombs put his hand on Manning's back and whispered something to him, eliciting a slight smile on the soldier's face.

Manning's sentencing hearing is set to begin Wednesday. Despite being cleared on the most serious charge, Manning faces up to 128 years in prison for his breaches of the espionage act.

Mr Coombs came outside the court to a round of applause and shouts of "thank you" from a few dozen Manning supporters.

"We won the battle, now we need to go win the war," Mr Coombs said of the sentencing phase. "Today is a good day, but Bradley is by no means out of the fire."

Supporters thanked him for his work. One slipped him a private note. Others asked questions about verdicts that they didn't understand.

Manning's family said they were disappointed in the guilty verdicts, but thanked supporters and defence attorneys, in a statement written by his aunt and released to The Guardian.

"While we are obviously disappointed in today's verdicts, we are happy that Judge Lind agreed with us that Brad never intended to help America's enemies in any way," it said. "Brad loves his country and was proud to wear its uniform."

They also thanked Manning's supporters, saying "Their support has allowed a young army private to defend himself against the full might of not only the US army but also the US government."

WikiLeaks denounced the verdict, saying it reflected "dangerous national security extremism from the Obama administration". Australian WikiLeaks founder Julian Assange called Manning "a hero", BBC News reports.

WikiLeaks said on Twitter that the conviction of Manning on several counts of espionage set a "very serious new precedent for supplying formation to the press".

Mr Assange held a press conference from London's Ecuadorian embassy, where he said he expected the verdict would be appealed.

"Bradley Manning's alleged disclosures have exposed war crimes, sparked revolutions and induced democratic reforms," Mr Assange said.

"He is the most important journalistic source the world has ever seen."

The best known US rights group, the American Civil Liberties Union reiterated its concern about the use of anti-spying laws to curtail government whistleblowers.

"While we're relieved that Mr Manning was acquitted of the most dangerous charge, the ACLU has long held the view that leaks to the press in the public interest should not be prosecuted under the Espionage Act," said Ben Wizner, director of the ACLU Speech, Privacy and Technology Project.

"Since Manning already pleaded guilty to charges of leaking information - which carry significant punishment - it seems clear that the government was seeking to intimidate anyone who might consider revealing valuable information in the future."

The verdict by judge Col. Denise Lind follows about two months of conflicting testimony and evidence.

Manning pleaded guilty earlier this year to lesser offences that could have brought him 20 years behind bars, yet the government continued to pursue the original, more serious charges.

Manning said during a pre-trial hearing in February he leaked the material to expose the US military's "bloodlust" and disregard for human life, and what he considered American diplomatic deceit. He said he chose information he believed would not the harm the United States and he wanted to start a debate on military and foreign policy. He did not testify at his court-martial.

Defence attorney David Coombs portrayed Manning as a "young, naive but good-intentioned" soldier who was in emotional turmoil, partly because he was a gay service member at a time when homosexuals were barred from serving openly in the US military.

He said Manning could have sold the information or given it directly to the enemy, but he gave them to WikiLeaks in an attempt to "spark reform" and provoke debate. A counterintelligence witness valued the Iraq and Afghanistan war logs at about $US5.7 million ($6.2 million), based on what foreign intelligence services had paid in the past for similar information.

Mr Coombs said Manning had no way of knowing whether al-Qaida would access WikiLeaks and a 2008 counterintelligence report showed the government itself didn't know much about the site.

The defence attorney also mocked the testimony of a former supervisor who said Manning told her the American flag meant nothing to him and she suspected before they deployed to Iraq that Manning was a spy. Mr Coombs noted she had not written up a report on Manning's alleged disloyalty, though had written ones on him taking too many smoke breaks and drinking too much coffee.

The government said Manning had sophisticated security training and broke signed agreements to protect the secrets. He even had to give a presentation on operational security during his training after he got in trouble for posting a YouTube video about what he was learning.

The lead prosecutor, Maj. Ashden Fein, said Manning knew the material would be seen by al-Qaida, a key point prosecutor needed to prove to get an aiding the enemy conviction. Even Osama bin Laden had some of the digital files at his compound when he was killed.

Some of Manning's supporters attended nearly every day of two-month trial, many of them protesting outside the Fort Meade gates each day before the court-martial. They wore T-shirts with the word "truth" on them, blogged, tweeted and raised money for Manning's defence. One supporter was banned from the trial because the judge said he made online threats.

Hours before the verdict, about two dozen demonstrators gathered outside the gates of the military post, proclaiming their admiration for Manning.

"He wasn't trying to aid the enemy. He was trying to give people the information they need so they can hold their government accountable," said Barbara Bridges, of Baltimore.

The court-martial unfolded as another low-level intelligence worker, Edward Snowden, revealed US secrets about surveillance programs. Snowden, a civilian employee, told The Guardian his motives were similar to Manning's, but he said his leaks were more selective.

Manning's supporters, including Australian WikiLeaks founder Julian Assange, believed a conviction for aiding the enemy would have a chilling effect on leakers who want to expose wrongdoing by giving information to websites and the media, and on journalists who publish the informaiton.

Before Snowden, Manning's case was the most high-profile espionage prosecution for the Obama administration, which has been criticised for its crackdown on leakers. The espionage cases brought since Mr Obama took office are more than in all other presidencies combined.

The WikiLeaks case is by far the most voluminous release of classified material in US history. Manning's supporters included "Pentagon Papers" leaker Daniel Ellsberg, who in the early 1970s spilled a secret US Defence Department history of US involvement in Vietnam.

The 7000 pages of the "Pentagon Papers" showed that the US government repeatedly lied to the public about the Vietnam War.

The material WikiLeaks began publishing in 2010 documented complaints of abuses against Iraqi detainees, a US tally of civilian deaths in Iraq, and America's weak support for the government of Tunisia - a disclosure that Manning supporters said helped trigger the Middle Eastern pro-democracy uprisings known as the Arab Spring.

The Obama administration said the release threatened to expose valuable military and diplomatic sources and strained America's relations with other governments.

Prosecutors said during the trial Manning relied on WikiLeaks and Assange for guidance on what secrets to "harvest" for the organisation, starting within weeks of his arrival in Iraq in late 2009.

Federal authorities are looking into whether Assange can be prosecuted. He has been holed up in the Ecuadorean Embassy in London to avoid extradition to Sweden on sex-crimes allegations.