The call was made after an analysis of outstanding ballots showed there was no way for Perdue, who was seeking a second term, to overtake Ossoff’s lead.
Tens of thousands of outstanding votes remain to be counted, but the vast majority were in six Democratic-leaning counties that Ossoff was winning.
Many of the ballots left to be counted were mail votes, a form of voting that overwhelmingly favored Ossoff.
The remaining votes left to be counted in Republican-leaning areas that favored Perdue were not enough for him to catch up.
Until Warnock, a Democrat hadn't won a U.S. Senate contest in the state since former Georgia Gov.