Democrats already have the majority in the 100-seat Senate – 50 compared to 49 for Republicans.
But Warnock being reelected would give them a 51-49 edge and no longer require going to Vice President Kamala Harris for the tie-breaker vote to pass legislation they support.
Warnock edged out football legend Walker in the midterm general election but failed to cross the 50%-of-the-vote threshold required by Georgia election law, triggering the runoff.
Warnock leads by as many as 5 percentage points, according to the most recent polls, in part because he, like many Democrats candidates in recent years, benefit from early voting.
Roughly 1.9 million votes have already been cast by mail and during early voting, according to the Associated Press.
Republicans, whose voters have traditionally relied more on voting on Election Day at polling stations, are optimistic that Walker will catch up Tuesday.
Voters in Fulton County, which is the state’s most populous county and includes the city of Atlanta, went to polls in the morning amid a cold, wet rain. But forecasts show the precipitation having ended by about 9 a.m. local time.
Warnock is the state’s first black senator and is the senior minister of the Atlanta church in which Martin Luther King Jr. preached.
Walker is a former NFL and University of Georgia football star and first-time political candidate backed by former President Trump.
His first campaign has been set back at times by off-message comments typical of a neophyte candidate and allegations that he paid for two former girlfriends’ abortions.
Walker has denied the allegations, and state Republican voters appear to have largely stuck by their candidate, as an underdog, and who like Warnock is a black male.
In addition to the early voting advantage, Warnock’s reelection campaign also has the money advantage, having spent roughly $170 million on the campaign, compared to $60 million for the Walker campaign, according to the most recent federal disclosures. That money does not include spending by the Democrat and GOP party committees and political action committees.
Georgia appears to continue to move from a reliable Republican-leaning state to a more of a battleground state.
Though the state now has two Democrat senators, Republicans swept every other statewide midterm contest, which includes the reelection of GOP Gov. Brian Kemp.
Warnock was elected to office in 2021 in a special election for the remainder of GOP Sen. Johnny Isakson’s term.
“They’ve seen that I will work with anybody that helps me to do good work for the people of Georgia,” said the 53-year-old senator, according to the wire service. “I think they’re going to get this right. They know this race is about competence and character.”
Walker barnstormed Monday with wife Julie, telling residents, “I love y’all. We’re gonna win this election.”