Wesley Bell, a St. Louis prosecutor, will be the party’s candidate for the state’s first congressional district in November.
Ms Bush rose to notoriety as an organizer in the Black Lives Matter movement and, after taking office in 2021, as a member of the “Squad” of Democratic House members recognized for supporting progressive causes.
She has been an outspoken critic of Israel’s assault in Gaza, and pro-Israel groups have spent more than $10 million (£7.9 million) to topple her in the primary.
Projections from both the Associated Press news agency and News predict that Mr Bell is on course to win the vote with 51%.
The district is largely Democratic, and Mr Bell is expected to retain it in the upcoming election.
According to reports, the American Israel Public Affairs Committee (Aipac) provided nearly all of the funds used to campaign against Ms Bush. Politico reported that Aipac, a pro-Israel lobbying group, has pledged to spend more than $100 million to defeat progressive politicians who have spoken out against the Gaza conflict.
The Squad, a group of nine progressive members in the United States House of Representatives, has suffered its second loss in recent months.
