Citing unnamed sources briefed on the defection, the network said Shahram Amiri, a nuclear physicist in his early 30s, defected as part of a long-planned operation to get him to leave Iran and resettle in the United States.
A CIA spokeswoman declined to comment.
Amiri, a university researcher working for Iran's Atomic Energy Organization, disappeared during a pilgrimage to Mecca in June, three months before Iran disclosed the existence of its second uranium enrichment site near the city of Qom.
In December, Tehran accused Saudi Arabia of handing Amiri over to the United States.
The ABC report said Amiri has been extensively debriefed since his defection and said he helped confirm US intelligence assessments about the Iranian nuclear program.