Republican Senator David Perdue and his Democratic challenger Jon Ossoff will head to a runoff in January after Perdue failed to receive at least 50% of the vote, according to an AP projection.
In Georgia, candidates must receive 50% of the vote to be elected. If they don't, the race goes to a runoff.
The state's other Senate race between Republican Senator Kelly Loeffler and Democratic candidate Raphael Warnock is also heading to a runoff.
Both races will be closely watched because control of the Senate is crucial for passing legislation and confirming judges in the US.
Democrats already have control of the House of Representatives and if they win the Senate, they would be able to more easily pass laws with full control of both chambers of Congress.
The state of Georgia has played a surprisingly central role in the 2020 election.
Traditionally, the state has voted Republican but this year, the state remains too close to call in the presidential race between President Donald Trump and Democratic candidate Joe Biden.
Georgia's Secretary of State has said it will likely head to a recount after Biden overtook Trump's lead after winning votes from the state's more urban areas.
Many Democrats have credited former Georgia gubernatorial candidate Stacey Abrams for registering new voters.
"We have seen progress being made. And I think absolutely we can not only deliver 16 Electoral College votes, we can deliver two U.S. Senate seats," Abrams said in October.
African-Americans make up more than 30% of the state's population and tend to vote Democratic.
Georgia runoff elections crucial for Democrats
Analysts believe the Republicans will keep control of the Senate, where they have had a majority since 2014.
Democrats would have needed to pick up three Senate seats in 2020, but so far, they have gained two seats, in Colorado and in Arizona, and lost one in Alabama.
If Biden wins the presidency, they still need two additional Senate seats to have a majority. This means that the two runoff elections in Georgia could be crucial for Democrats.
Senator Bernie Sanders, a former Democratic nominee, said Democrats needed to win the two Senate seats in Georgia because much work was needed to be done to tackle crises in the country.