Polls open at 7:00 am (1200 GMT) in the southern state. A record three million-plus people have voted early, election officials say, and final results may not be known for several days.
If Democrats flip both seats they will win back the Senate, effectively handing Biden all levers of political power in Washington and helping him enact his ambitious legislative agenda.
"One state -- one state! -- can chart the course, not just for the next four years but for the next generation," Biden told a rally in Atlanta where he campaigned on Monday with the two Democrat contenders.
I’m asking you to give everything you’ve got for one more day — because that one day can change America.https://t.co/RIJ1L4B5o9 pic.twitter.com/6RvV9Ffx04
— Joe Biden (@JoeBiden) January 5, 2021
'Last chance to save America'
Republicans argue that keeping Senate control would serve as a check on the incoming Biden administration.
"The stakes in this election could not be higher," out-going President Donald Trump told a raucous rally in Dalton, Georgia hours after Biden's Atlanta speech. "Make sure your vote is counted."
The races feature Republican incumbent senators Kelly Loeffler and David Perdue, both wealthy businesspeople-turned-politicians, against Black pastor Raphael Warnock and documentary producer Jon Ossoff.
Noting that "the whole world is watching," Trump implored Georgians to re-elect the Republicans. Tuesday's runoffs are "your last chance to save the America that we love," he said.
