He was found guilty of 19 of 22 charges for illegal release of documents, including five counts of espionage.
He could still face up to a maximum of more than 150 years in prison if the judge decides to compound the maximum sentences of the more minor charges.
Manning, 25, worked as an intelligence analyst for the Army and his leak is still the largest release of sensitive government documents in U.S. history. He was arrested in May 2011 and imprisoned since.
The massive cache included about 250,000 diplomatic cables, thousands of incident reports from Iraq and Afghanistan and videos showing U.S. airstrikes killing civilians.
In December 2012, Manning pleaded guilty to 10 lesser charges, carrying a maximum sentence of 16 years. Army Col. Denise Lind, the judge, determined in January that sentence would be reduced to a maximum 112 days, based on his treatment while imprisoned at Quantico Marine Corps Brig.
Although Manning admitted to the basic facts of the disclosures, prosecutors pressed forward with the more serious charges and tried -- and apparently failed -- to prove he released the information while knowing it would end up in the hands of al Qaeda.
The trial was carefully watched by press freedom advocates, who feared a conviction of aiding the enemy would endanger protected practices by journalists and the whistle-blowers who inform them. Even the charge, regardless of conviction, casts a long shadow: Leaking classified documents to newspapers can now be legally sufficient to merit an "aiding the enemy" charge.
The sentencing phase of the trial will begin Thursday.