The eight-member military jury found the defendant guilty of premeditated murder and conspiracy to commit premeditated murder after a three-day trial.
Hatley, 40, was acquitted of another murder in January 2007 of an Iraqi opposition fighter, who medics said was shot when already close to death.
Derrick Grace, the army prosecutor, said testimony had conveyed "a complete breakdown of discipline and crimes that are among the worst of a soldier".
"On two separate occasions, the accused became the judge, jury and executioner," he said.
Hatley will be sentenced on Thursday at the US army's Rose Barracks in southern Germany and faces up to life in prison without parole.
He had pleaded not guilty and showed no emotion on hearing the verdict, after which he embraced his wife, fellow soldiers and friends.
'No physical evidence'
The incident for which Hatley was convicted occurred in March or April 2007, when Hatley's unit had exchanged fired with a group of four Iraqis.
Weapons were then found in a building the four had fled to, and the men were taken into custody.
Hatley was accused of overseeing the shootings of the detainees and telling his colleagues that they were to "take care" of them and kill them.
The defence asserted that there was no physical evidence of the deaths as no bodies, witnesses or blood have been found.
Hatley was the highest ranking of three soldiers tried for killing the prisoners, the other two were convicted of the murders separately earlier this year.
Two other soldiers were also convicted of involvement in the spring 2007 incident.
All were with the 1st battalion, 18th infantry regiment, 2nd brigade, 1st infantry division in Baghdad. The unit is now part of the Germany-based 172nd infantry brigade.
Hatley had previously served in the first Gulf War and Kosovo.