Why It Matters: Her defection makes her the first Black woman to serve as a Republican in the body.
Ms. Mainor, 48, is the first Black woman to hold office as a Republican in Georgia’s state house, according to Stewart Bragg, director of the Georgia House Republican caucus.
Her defection recalled the political estrangement of another former Democratic lawmaker in Georgia: Vernon Jones, a Republican who was endorsed by former President Donald J. Trump in his unsuccessful run for Congress in 2022.
Background: She has a recent history of siding with Republicans.
Ms. Mainor had crossed the aisle on several notable occasions before she switched parties altogether.
When Republicans tried to expand a school voucher program this year, she cast the lone Democratic vote in support of the bill, which failed.
In 2021, Ms. Mainor was one of three Democrats in the House who backed a G.O.P. bill that curbed the powers of counties to reduce funding for the police. The measure was signed into law by Gov. Brian Kemp, a Republican.
She also sided with Republicans this spring in the creation of a state oversight commission that has the power to investigate and remove local prosecutors.
At the news conference on Tuesday, Ms. Mainor said Democrats no longer shared the values that had drawn her to the party.
“Members of the Democrat Party have publicly slandered me in every way imaginable,” she said.
What’s Next: It may be hard for her to hold on to the seat.
Democrats disavowed Ms. Mainor on Tuesday as a rogue lawmaker and pledged to challenge her next year.
“Good riddance,” Josh McLaurin, a state senator from Fulton County, wrote on Threads.
While Ms. Mainor won a primary against two other Democrats last June with 65 percent of the vote, she did not face an opponent in the November election in 2020 and 2022.
It’s tough sledding for Republicans in Fulton County, which Joseph R. Biden Jr. won with 72.6 percent of the vote in the 2020 election.