With 99% of the estimated vote counted, he led Walker by 50.8% to 49.2%, according to Edison Research.
The result cements Georgia as a battleground state certain to play a prominent role in the 2024 presidential election.
Senator Raphael Warnock (D-GA) speaks during an election night party after a projected win in the U.S. midterm runoff election between Warnock and his Republican challenger Herschel Walker in Atlanta, Georgia, U.S., December 6, 2022.
It is his second runoff victory in two years, after he won the seat in January 2021.
Venkayla Haynes, 28, said Warnock's win was especially meaningful after months of organizing get-out-the-vote efforts for both the general election and then the runoff.