Attorney Hank Johnson, a former county commissioner, won the nomination with 59 percent of the vote, surpassing McKinney by more than 11,000 votes. Johnson is likely to win in the fall in the heavily Democratic district.
After claiming victory, he told cheering supporters, "I'm going to make you proud."
In a bizarre concession speech early Wednesday morning, McKinney criticized the news media, claimed electronic voting machines were a threat to democracy and refused to congratulate Johnson by name.
"We aren't going to tolerate any more stolen elections," she said. "We're watching you and we want our leaders back or we will become the leaders."
McKinney, her state's first black congresswoman, has long been controversial. Her suggestion that the Bush administration had advance knowledge of the Sept. 11, 2001, terror attacks helped galvanize opposition and she lost her seat in 2002, but won it again two years ago.
In her latest brouhaha in March, she struck a Capitol police officer who did not recognize her and tried to stop her from entering a House office building.
A grand jury in Washington declined to indict her, but she was forced to apologize before the House. She drew 47 percent of the vote in last month's primary.
It was the second time in three election years that McKinney has been upset. After 10 years in Congress, she first lost in the 2002 primary to political newcomer Denise Majette, who vacated the seat two years later to run for the U.S. Senate. McKinney emerged from a crowded 2004 Democratic primary to easily reclaim the seat.
University of Georgia political science professor Charles Bullock said McKinney's political career has come to an end.
"She's history. You don't get another chance to come back after losing two primaries," said Bullock. "It's rare to come back after losing once."
In other election results Tuesday:
Democratic Gov. Jennifer Granholm and Republican multimillionaire Dick DeVos faced no opposition in their primaries.