In 2018, a Democratic gun control and racial justice activist named Lucy McBath flipped a Republican-held Georgia congressional seat that, in a different configuration, had once been held by Newt Gingrich.

In 2020, a college professor named Carolyn Bourdeaux prevailed in another suburban Atlanta district a little farther east, becoming the only Democratic House candidate to flip a seat in the general election that year.

And now, Ms. McBath and Ms. Bourdeaux — two female lawmakers who have similar voting records and reflect the ascendant Democratic coalition in Georgia — are on a collision course, battling to represent the state’s newly redrawn Seventh District in a House member-versus-member primary election on Tuesday.

“It’s a shame that we had to choose between them,” said Andrew Young, a former congressman, U.S. ambassador to the United Nations and mayor of Atlanta. “But that is the kind of trickery that went into reapportionment.”

Mr. Young has endorsed Ms. Bourdeaux, though he said his wife was rooting for Ms. McBath.

Under the once-in-a-decade redistricting process, Georgia’s Republican governor, Brian Kemp, signed into law a new map that transformed Ms. McBath’s district to favor Republicans overwhelmingly. Ms. Bourdeaux’s nearby district, the Seventh, became strongly Democratic, and Ms. McBath chose to run there.

The result is a matchup that has left party leaders in the district anguished — one of several bruising House primaries around the country pitting incumbents against one another in newly drawn districts.

In Georgia, many Democrats fault Republican machinations around the reapportionment process for, in their view, effectively squeezing out an incumbent House Democrat.

At a virtual rally Thursday night, Ms. McBath implicitly cast her decision to run in the Seventh District as a rebuke to the Republicans, declaring that she “refused to let the Republicans silence me.”

State Representative Donna McLeod, who is campaigning energetically but lags in fund-raising, is also running in the contest, which could head to a runoff.

The intraparty battle comes roughly a year and a half after Georgia, a longtime Republican bastion, not only helped deliver the presidency to the Democrats, but also elected two Democratic senators, cementing the party’s Senate majority. Those victories were propelled by a broad constellation of constituencies, including a surge in turnout by Black Georgians and a thorough rejection of Donald J. Trump in the state’s diverse suburbs.

Ms. McBath is a Black woman from the suburbs of Atlanta who has been embraced by several liberal organizations and some progressives like Senator Elizabeth Warren of Massachusetts, but she is not typically seen as a left-wing candidate. Ms. Bourdeaux, a white moderate, was also skilled at appealing to those in historically center-right territory. Both represent, in many ways, parts of the sprawling Biden coalition that Democrats are straining to hold together headed into a challenging midterm election season.

Ms. Bourdeaux is regarded as the more centrist candidate in the race. She joined other House moderates, for instance, in saying she would not support a budget resolution meant to pave the way for President Biden’s sweeping social policy package until a bipartisan infrastructure measure became law, a stance that outraged many Democrats who had planned to pair the priorities.

But in contrast to Democratic primaries elsewhere, the primary contest in Georgia’s Seventh District has not been a searing ideological fight over the direction of the party, or a race dominated by negative advertising. Both women emphasize issues like protecting abortion rights and voting rights, and they received a joint endorsement from the Planned Parenthood Action Fund.

Yet there are clear stylistic and strategic differences as they vie to represent a racially and ethnically diverse district.

Ms. McBath, widely regarded as the front-runner, is running on her personal story, recently earning national attention from prominent Democrats, including former Secretary of State Hillary Clinton, for her starkly emotional testimony about her struggles with pregnancy as she advocated for abortion rights.

Linking to a video clip of Ms. McBath, Mrs. Clinton wrote on Twitter: “Please listen to @RepLucyMcBath as she speaks for so many women who have had miscarriages and stillbirths — tragic losses the right wing seeks to criminalize.”

Ms. McBath is perhaps best known for her activism after her teenage son, a young Black man, was shot and killed by a white man in 2012 over the volume of the rap music playing in his car. The man was later convicted of first-degree murder.

Pro-McBath advertising highlights her work on gun violence prevention and her experience with tragedy, in spots run by her campaign and by supportive outside groups, including two groups associated with former Mayor Michael R. Bloomberg of New York: Independence USA PAC, his personal super PAC, and the political arm of Everytown for Gun Safety, a group Ms. McBath has worked for.

She also has the backing of the super PAC Protect Our Future, bankrolled by the crypto billionaire Sam Bankman-Fried.

Lewanna Heard Tucker, the Democratic chair in Fulton County, Ga., said that she was receiving three or four McBath fliers a week, and that she believed friends of hers were receiving similar numbers from Ms. Bourdeaux.

“It’s going to be a battle to the end,” she said. “It’s definitely a rough situation for Democrats to be in, because we like both candidates.”

In an interview, Ms. Bourdeaux cast the race as a choice between a member of Congress who has forged deep relationships in the district, and a national star whose local connections are more tenuous. She also faulted Ms. McBath for switching districts to run.

“If you look at who I’m endorsed by, it is the people in the community,” Ms. Bourdeaux said. “It really is very much this very local race.”

She added, “I really have done a lot for the community, up against someone who is a celebrity.”

Ms. McBath has toured small businesses, and on Friday she appeared with another prominent Democrat: former Representative Gabrielle Giffords of Arizona, who was shot in the head in 2011 and now works to battle gun violence.

Ms. McBath and her campaign declined to comment for this article.

“Lucy has just been someone that we are excited about,” said Glynda C. Carr, the president and C.E.O. of Higher Heights for America PAC, an organization focused on electing Black women that has endorsed Ms. McBath. But, she said, whoever prevails, “that region is going to mourn the loss of a representative and a champion.”