The former intelligence analyst was convicted of 20 of 22 charges for sending hundreds of thousands of government and diplomatic secrets to the anti-secrecy website, but he was found not guilty of aiding the enemy, which alone could have meant life in prison without parole.
"We're not celebrating," said defense attorney David Coombs. "Ultimately, his sentence is all that really matters."
The judge prohibited both sides from presenting evidence during trial about any actual damage the leaks caused to national security and troops in Afghanistan and Iraq, but lawyers will be allowed to bring that up at sentencing. Read: Bradley Manning pleads guilty in WikiLeaks case, faces 20 years
The release of diplomatic cables, warzone logs and videos embarrassed the US and its allies, but it was unclear how much damage it caused to national security beyond that. US officials warned of dire consequences in the days immediately after the first disclosures in July 2010, but a Pentagon review later suggested those fears might have been overblown.
The judge also restricted evidence about Manning's motives. Manning testified during a pre-trial hearing that he leaked the material to expose US military "bloodlust" and diplomatic deceitfulness, but did not believe his actions would harm the country. He didn't testify during the trial, but he could take the stand during the sentencing phase.
Army Pfc. Bradley Manning is escorted to a security vehicle outside a courthouse in Fort Meade after a court martial hearing. (AP Photo)
He faces up to 136 years in prison If given maximum penalties in the sentencing phase which is expected to last most of August.
Lisa Windsor, a retired Army colonel and former judge advocate, said the punishment phase would focus on Manning's motive and the harm that was done by the leak.
"You're balancing that to determine what would be an appropriate sentence. I think it's likely that he's going to be in jail for a very long time," said Windsor, now in private practice in Washington.
The judge, Army Col. Denise Lind, deliberated three days before reaching her verdict in a case involving the largest leak of documents in US history. The case drew worldwide attention as supporters hailed Manning as a whistleblower and the US government called him an anarchist computer hacker and attention-seeking traitor. Read: Evidence suggests Manning leaked sensitive names
The verdict denied the government a precedent that freedom of press advocates had warned could have broad implications for leak cases and investigative journalism about national security issues.
Whistleblower advocates and legal experts had mixed opinions on the implications for the future of leak cases in the Internet age.
The advocacy group Reporters Without Borders said the verdict was a chilling warning to whistleblowers, "against whom the Obama administration has been waging an unprecedented offensive," and threatens the future of investigative journalism because intimidated sources might fall quiet.
However, another advocate of less government secrecy, Steven Aftergood of the Federation of American Scientists, questioned whether the implications will be so dire, given the extraordinary nature of the Manning case.
"This was a massive hemorrhage of government records, and it's not too surprising that it elicited a strong reaction from the government," Aftergood said.
"Most journalists are not in the business of publishing classified documents, they're in the business of reporting the news, which is not the same thing," he said. "This is not good news for journalism, but it's not the end of the world, either."
Glenn Greenwald, the journalist, commentator and former civil rights lawyer who first reported Edward Snowden's leaks of National Security Agency surveillance programs, said Manning's acquittal on the charge of aiding the enemy represented a "tiny sliver of justice."
But WikiLeaks founder Julian Assange, whose website exposed Manning's spilled US secrets to the world, saw nothing to cheer in the mixed verdict.
"It is a dangerous precedent and an example of national security extremism," he told reporters at the Ecuadorean Embassy in London, which is sheltering him. "This has never been a fair trial."
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.
Manning pleaded guilty earlier this year to lesser offenses that could have brought him 20 years behind bars, yet the government continued to pursue all but one of the original, more serious charges.
Rep. Howard "Buck" McKeon, chairman of the House Armed Services Committee, welcomed Tuesday's verdict.
"Bradley Manning endangered the security of the United States and the lives of his own comrades in uniform when he intentionally disclosed vast amounts of classified data," the Republican congressman said. "His conviction should stand as an example to those who are tempted to violate a sacred public trust in pursuit of notoriety, fame, or their own political agenda."
Manning acknowledged giving WikiLeaks more than 700,000 battlefield reports and diplomatic cables, and video of a 2007 US helicopter attack that killed civilians in Iraq, including a Reuters news photographer and his driver. Prosecutors branded him an anarchist and traitor. The defense portrayed the Crescent, Oklahoma, native as a "young, naive but good-intentioned" figure.
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. Read: Manning was naive, but good-intentioned, says attorney
To prove aiding the enemy, prosecutors had to show Manning had "actual knowledge" the material he leaked would be seen by al-Qaida and that he had "general evil intent." They presented evidence the material fell into the hands of the terrorist group and its former leader, Osama bin Laden, but struggled to prove their assertion that Manning was an anarchist computer hacker and attention-seeking traitor.
The judge did not give any reasons for her verdict from the bench, but said she would release detailed written findings. She did not say when.
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, whose sensational leak of 7,000 pages of documents in the early 1970s exposed US government lies about the Vietnam War.
Reacting to Tuesday's verdict, Ellsberg said Manning's acquittal on aiding the enemy limits the chilling consequences of the WikiLeaks case on press freedoms.
"American democracy just dodged a bullet, a possibly fatal bullet," Ellsberg said. "I'm talking about the free press that I think is the life's blood of the democracy."