The beaten detainee later died, but David Passaro, 40, was not charged in his death. The federal jury found him guilty after about eight hours of deliberations of three counts of simple assault and one count of assault resulting in serious bodily injury.
Passaro faces up to 11½ years in prison. No sentencing date was set.
Passaro was the first American civilian to be charged with mistreating a detainee during the wars in Iraq and Afghanistan. He was accused of beating Abdul Wali while the man was being questioned in 2003 about rocket attacks on a remote base where Passaro was stationed with U.S. and Afghan troops.
"Today, a North Carolina jury sitting here in Raleigh delivered a message to the world and that is that no one is above or beneath the laws of the United States of America," said acting U.S. Attorney George Holding. "This should be a message to the world that wherever U.S. laws are ruling today, justice will be done."
Passaro was impassive as the jury verdict was read. After jurors left the courtroom, he stood up and quietly extended his wrists so federal marshals could handcuff him.
"Dave was disappointed in the verdict. We're going to keep on fighting," said defense lawyer Joe Gilbert. He declined to say if Passaro planned to appeal.
Members of Passaro's church watched from the gallery as the verdict was read, and a retired minister leading the small group from Flat Branch Presbyterian Church in Bunn Level said they continue to support him.
"David will be strong," Bert Pitchford said. "He has good faith."
Passaro was a civilian employed by the CIA. He was stationed in a remote base in Afghanistan manned by American and Afghan forces, CBS News Raleigh, N.C., affiliate WRAL reports.
Lawyers painted vastly different pictures of the defendant during the trial.
Prosecutor Jim Candelmo said Passaro beat Wali "mercilessly for 48 hours before he died" as he tried to get information about rocket attacks on the Asadabad base in remote northeastern Afghanistan.
"This is a flashlight," Candelmo told the jury. "It is used by many of you and me to illuminate a path in the darkness. ... He used it as a bludgeon.
"Why is he hitting him? To inflict pain to get him to talk."
Defense lawyer Gilbert argued that Passaro tapped Wali with the flashlight.
"Basically, Dave lost the game of musical chairs," he said. "We wouldn't be here if this terrorist hadn't died."
Candelmo said fingerprints from the flashlight batteries linked Passaro to the crime. Pathologists testifying for the prosecution and the defense disagreed over whether photos of Wali's body and testimony from guards show that the prisoner probably died from beatings.
Prosecutors had charged Passaro with two counts of assault with a dangerous weapon with intent of bodily harm and two counts of assault resulting in serious bodily injury. The jury instead convicted him of lesser charges, an option the judge offered during jury instructions.
Passaro was tried under a provision of the USA Patriot Act that allows charges against U.S. citizens for crimes committed on land or facilities designated for use by the U.S. government.