Polls officially closed at 7 p.m. ET — with the exception of two locations that remained open for an extra 30 minutes after experiencing technical issues.
The race pitted 30-year-old Democrat and political neophyte Jon Ossoff against Handel, who is Georgia's former Secretary of State.
The Daily Beast's Patricia Murphy tweeted that as the returns came in, Ossoff's volunteers and staff were "visibly shocked."
Ossoff called Handel to concede the race after results made it clear she would emerge the winner. In a fiery speech he gave afterward, Ossoff thanked his supporters in the district, which he said he become "the epicenter of politics" in recent months.