The Associated Press called the race for Ossoff shortly after 4:00 p.m. EST, and other networks followed.
Ossoff leads Perdue by less than 0.6 percentage points, a slim margin but just over the 0.5-percentage-point threshold that would trigger an automatic recount of the vote.
Ossoff’s victory comes after Raphael Warnock was projected to win the other runoff race in Georgia, defeating Republican Kelly Loeffler.
The victories for Ossoff and Warnock means the Senate will be tied at 50-50, allowing Vice President-elect Kamala Harris to use her tie-breaking vote to give control of the upper chamber to Democrats.
Warnock will become Georgia’s first Black US senator and Ossoff, who is Jewish, will become the Senate’s youngest member at 33 years of age.
Ossoff first rose to national political prominence during his 2017 campaign for a suburban-Atlanta House seat in a special election.
The race between Ossoff and Perdue, whose first term in the Senate expired Sunday, advanced to a runoff after neither candidate surpassed the 50 percent threshold needed to win outright in November.
Warnock has come under fire for controversial remarks related to Israel that he made in a 2018 sermon at his church, when he asserted that Israel "shoots unarmed Palestinians".
He walked back those remarks last month, saying he had an “increasing recognition” of the danger that Hamas poses to Israel since his harsh criticisms of Israel in that sermon. Warnock also said he opposed the anti-Israel Boycott, Divestment and Sanctions (BDS) movement.