Minnesota Rep. Michele Bachmann, who won prominence as a leader of the tea-party opposition to President Barack Obama, announced Wednesday she wouldn't seek re-election—an abrupt retreat less than two years after she briefly topped the ranks of GOP candidates seeking the 2012 presidential nomination.

Mrs. Bachmann's bid for the White House raised her national profile but also contributed to her political troubles. She barely won re-election to her House seat last year and has since seen inquiries begin into the financial activities of her presidential campaign.

Her fans and foes agree that Mrs. Bachmann has had broad political impact by helping to elevate the tea party's voice in Congress in its earliest days, when she embraced its founding cause—opposition to Mr. Obama's health-care law—as her own. "She helped to grow and convert the tea party from a protest movement into a political movement," said Sal Russo, co-founder of Tea Party Express, a national tea-party group.

But her combative tone drew complaints that it intensified political partisanship. Her "tea-party brand of extremism and obstruction have infected the entire Republican Congress, and her influence shows no signs of waning," said Democratic Congressional Campaign Committee spokeswoman Emily Bittner.

Mrs. Bachmann's departure comes amid a change in the public face of the tea party on Capitol Hill, as she has been eclipsed by newcomers that include Sens. Mike Lee of Utah and Ted Cruz of Texas, and Rep. Raúl Labrador (R., Idaho), who seem more inclined to shake up the congressional system from within. Mr. Labrador, for example, is trying to make a legislative mark as member of a group negotiating a bipartisan immigration bill.