The election, which sees both races tightly contested, will decide which party takes control of the Senate.
“We agree that our ad tools are an important way for people to get information about these elections,” wrote Facebook’s Sarah Schiff in a blog post.
“So we have developed a process to allow advertisers to run ads with the purpose of reaching voters in Georgia about Georgia’s runoff elections.”
Republicans currently hold a 50-48 majority in the Senate.
If the two Democrat challengers win both of the Georgia elections, Vice President-elect Kamala Harris would cast the tie-breaking vote, giving the party full control of the White House and both chambers of Congress.
But if Republicans win one of the seats they will retain control of the Senate.
Facebook says it will prioritise advertisers with “direct involvement in these elections” and reject adverts targeting locations outside the state.
Before the general election the company announced it would stop running political adverts after the polls closed on 3 November amid fears of disinformation campaigns.
Before the reversal groups could not use the platform to raise money or promote the candidates in Georgia.