The Lost star will appear in the final two episodes of the TNT's drama second season, Entertainment Weekly reports.
He will play a former history professor and mentor to Tom (Noah Wyle).
As well as starring in Lost, O'Quinn has had roles in shows such as JAG, Alias and The West Wing.
Most recently, he had a part in Hawaii Five-0.
Falling Skies, which was renewed for a second season last July, will return to TNT this summer.