Handel's victory was welcomed by the Republican Party and U.S. President Donald Trump, after Democrats hoped to win this traditionally Republican district, which held a special election after its previous Congressman, Republican Tom Price, was chosen by Trump to be his Secretary of Health and Human Services.
Those trends leave Democrats hopeful they can win a House majority next year. Instead, they watched in disbelief as the Republican candidate, Karen Handel, won handily in a race that some Democrats had said might well be a "referendum" on the Trump Administration.
Georgia voters have steadily streamed into Atlanta polling stations to decide the most expensive House race in USA history.
Actor John Leguizamo's assertion that democracy itself hinged on Ossoff winning underscored how desperate Hollywood was to send a resounding message of resistance to Trump's presidency.
Speaking after her win, Handel said her first priorities in Congress will be finishing the GOP health-care bill and working to lower corporate and individual tax rates. President Trump has also fundraised on her behalf and given his support on Twitter.
Handel sought to keep the president at arm's length, although her platform included priorities similar to Trump's.
The affluent and well-educated district has elected former House Speaker Newt Gingrich; Johnny Isakson, now Georgia's senior US senator; and most recently Tom Price, who resigned in February to join Trump's administration. Ossoff needs a tie there to have a chance of winning, strategists involved in the race say. Trump tweeted early Tuesday that Ossoff will raise taxes, is weak on crime and "doesn't even live in (the) district".
Trump weighed in on the election early on Tuesday morning.
CNN has forecast that Ms Handel has won the race by 52.4 percent to Mr Ossoff's 47.6 percent.
But an Ossoff victory would help Democrats raise money and recruit candidates as they try to win back control of the House of Representatives in 2018.
Actresses Sarah Silverman and Debra Messing attacked Ossoff's opponent, Karen Handel, on social media in the run-up to Tuesday's election. Ossoff also served U.S. Rep. Hank Johnson as a a national security staffer. However, the results were closer than expected, according to analysts.
Special election results are trickling in, county by county.
Meanwhile, Republican Ralph Norman won a special legislative election in SC against Democrat Archie Parnell. A staunchly Republican seat, the sixth district of Georgia has been held by Republicans since 1979.
Ossoff said he lives "a mile and a half down the street" from the district. He has said the address is close to Emory University, where his fiancee attends medical school.
Handel and tens of millions of dollars in ads from GOP super PACs called Ossoff an inexperienced liberal who has more in common with California than Georgia.
Democrats hoped Ossoff could pull off an upset after falling just short of the 50 percent needed in April to avoid today's runoff election.