Warnock addressed his supporters shortly after the polls closed and declared victory.
"Georgia I am honored by the faith that you have shown in me and I promise you this tonight, I am going to the Senate to work for all of Georgia," Warnock said short.
The focus now shifts to the second race between Sen. David Perdue and Democrat Jon Ossoff. The candidates were locked in a tight race and it was too early to call a winner. Under Georgia law, a trailing candidate may request a recount when the margin of an election is less than or equal to 0.5 percentage points.
If Ossoff wins, Democrats will have complete control of Congress, strengthening President-elect Joe Biden's standing as he prepares to take office on Jan. 20.
Loeffler encouraged her supporters to "keep fighting." She refused to concede. Loeffler told supporters her campaign saw a path to victory.
"Every single American, stay in the fight with us," Loeffler said after midnight, with votes still being counted. "We are going to keep fighting for you. This is about protecting the American dream. I'm never going to stop fighting for this country, for the American, for each one of you so that every Georgian has a voice in Washington.
"I work for you, I don't owe anyone up there anything," she continued. "We're going to get this done. God bless you, thank you so much, God bless Georgia and we are going to get this done. Thank you."
Stacey Abrams, the influential Georgia Democrat, congratulated Warnock on Twitter.
"Last January, I endorsed my dear friend in his quest to serve. Soon, he will walk those august halls & cast votes as a leader with courage, justice and integrity. God bless you and keep you in your service to us all," she wrote.
Fox News' Edmund DeMarche contributed to this report