Representative Kevin Kiley, a former Republican who changed his registration and became an independent earlier this year, will face Richard Pan, a former Democratic state senator, in California’s newly redrawn Sixth Congressional District this fall.

Mr. Kiley and Mr. Pan were the top vote-getters in a seven-way open primary, according to The Associated Press.

The new district includes the City of Sacramento and is widely considered to be favorable for Democrats.

Mr. Kiley was first elected to the House in 2022 to represent a more rural stretch of Northern California.

Even after he dropped his Republican affiliation, Mr. Kiley received large campaign donations from Republican groups, including a political action committee tied to House Speaker Mike Johnson.

When he changed his registration to “No Party Preference” in March, Mr. Kiley said he was frustrated by the ways partisanship was “weakening the country.” Although President Trump endorsed him in 2022, Mr. Kiley split from the Republican leadership several times last year. Last fall, he was among a few Republicans who showed up in Washington during the government shutdown.

While Mr. Kiley has had a significant financial advantage over his Democratic opponents, he has an uphill battle in a district where Democrats outnumber Republicans 3 to 1. Earlier this year, Mr. Kiley introduced a bill to ban mid-decade redistricting, but the bill has not been called up for a vote.

“Gerrymandering seeks to elevate partisanship above everything else in our politics,” he said at the time, adding that the best way to stop “insidious impacts on democracy is simply to take partisanship out of the equation.”

Mr. Pan is a pediatrician and former state lawmaker known for passing bills to toughen school vaccine requirements. Mr. Pan, who also teaches public health at the University of California, Davis, has said he wants to fight the Trump administration’s efforts to scale back health care and to push back on attacks on longstanding medical consensus.