Lucy McBath, the gun control and racial justice activist whose son was killed in a 2012 shooting, is now headed to Congress, after winning a razor-thin election decided Thursday morning.

Ms. McBath defeated the Republican incumbent Karen Handel, who only last year won a closely watched special election in the same Georgia district. Though Ms. Handel did not concede the race until Thursday morning, Ms. McBath, who is also a former Delta flight attendant, claimed victory in a statement released Wednesday. The Associated Press officially called the race for Ms. McBath on Thursday morning, with her lead at just under 3,000 votes.

“Six years ago I went from a Marietta mom to a mother on a mission,” she said, referencing her teenage son’s death. Jordan Davis, Ms. McBath’s son, was 17 when he was shot and killed by a white man at a gas station after refusing to turn down the volume of the rap music playing in his car. The man was later convicted of first-degree murder.