The military judge hearing the case, Army Col. Denise Lind, announced the verdict Tuesday. The charge was the most serious of 21 counts. It carried a possible life sentence without parole.
Manning was convicted of five espionage counts, five theft charges, a computer fraud charge and other military infractions.
Manning’s sentencing hearing is set to begin Wednesday.
The 25-year-old Crescent, Okla., native acknowledged giving the anti-secrecy website hundreds of thousands of battlefield reports, diplomatic cables and videos in early 2010.
Manning said he didn’t believe the information would harm troops in Afghanistan and Iraq or threaten national security.