The judge deliberated for about 16 hours over three days before reaching her decision in a case that drew worldwide attention. Supporters have hailed the 25-year-old Manning as a whistleblower. The U.S. government has called him an anarchist computer hacker and attention-seeking traitor.
The WikiLeaks case is by far the most voluminous release of classified material in U.S. history. Manning's supporters included Pentagon Papers leaker Daniel Ellsberg, who in the early 1970s spilled a secret Defense Department history of U.S. involvement in Vietnam that showed that the government repeatedly misled the public about the war.
Manning's sentencing begins Wednesday. He was convicted on 19 of 21 charges. The charge of aiding the enemy had carried a potential life sentence.
Manning stood at attention as the judge read the verdicts. He appeared not to react, though his attorney, David Coombs, smiled faintly when he heard not guilty on aiding the enemy. When the judge was done, Coombs put his hand on Manning's back and whispered something to him, bringing a slight smile to the soldier's face.
"We won the battle, now we need to go win the war,'' Coombs, outside court, said of the sentencing phase.
"Today is a good day, but Bradley is by no means out of the fire.''
Manning's trial was unusual because he acknowledged giving WikiLeaks more than 700,000 battlefield reports and diplomatic cables, plus video of a 2007 U.S. helicopter attack that killed civilians in Iraq and a Reuters news photographer and his driver. In the footage, airmen laughed and called targets ``dead bastards.''
Manning has said he leaked the material to expose the U.S 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 trial.
Manning pleaded guilty earlier this year to lesser offenses that could have brought him 20 years behind bars, yet the government continued to pursue the original, more serious charges.
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 U.S. military.
Coombs 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 $5.7 million, based on what foreign intelligence services had paid in the past for similar information.
Coombs said Manning had no way of knowing whether al-Qaida would access the secret-spilling website, and a 2008 counterintelligence report showed the government itself didn't know much about the site.
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 in Pakistan when he was killed.
Manning's supporters 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. The Defense Department has made it harder for one person acting alone to download material from a classified network and place it on an unclassified one.
U.S. officials warned of dire consequences in the days immediately after the first WikiLeaks disclosures in July 2010, but a Pentagon assessment determined in August 2010 that the leaks had not compromised intelligence sources or practices, although it said the disclosures could still cause significant damage to U.S. security interests.
The Manning trial unfolded as another low-level intelligence worker, Edward Snowden, revealed U.S. secrets about surveillance programs. Snowden, a civilian employee, has told The Guardian newspaper his motives were similar to Manning's, but he said his leaks were more selective.
Before Snowden, Manning's case was the most high-profile espionage prosecution for the Obama administration, which has been criticized for its crackdown on leakers. The espionage cases brought since Obama took office are more than in all other presidencies combined.
The material WikiLeaks began publishing in 2010 documented complaints of abuses against Iraqi detainees, a U.S. 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 its founder Julian Assange for guidance on what secrets to "harvest'' for the organization, 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.