Republicans have secured the 218 seats needed for a majority in the lower chamber of Congress a week after the midterm elections, the BBC's US partner CBS News projects.
While the party's margin in the House of Representatives is razor-thin, it is enough to stall President Joe Biden's agenda for the next two years.
Kevin McCarthy, the Republicans' leader in the House, celebrated the result.
But Democrats will retain control of the upper chamber, the Senate.
The new Congress will convene in January.
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The Republicans - who had hoped to win back control of both chambers - underperformed expectations in last week's midterms.
But they won the seat they needed for their House majority on Wednesday when California's 27th district went to incumbent Mike Garcia.
The Republican party is now projected to win between 218-223 seats in the 435-seat House, according to CBS.
But with votes in several cliff-hanger races still being counted, their majority may not be clear for days or even weeks.
Mr McCarthy, who was picked by rank-and-file Republicans on Tuesday to be their nominee to replace Democrat Nancy Pelosi as the next Speaker of the House, said the chamber had been "officially flipped".
"Americans are ready for a new direction, and House Republicans are ready to deliver," the California congressman tweeted on Wednesday night.
In order to be elected Speaker, the House Republican minority leader must win over majority support from the 435 members of the full House.
But Mrs Pelosi signalled she would not relinquish the gavel quietly, vowing in a statement on Wednesday night that her party would exert "strong leverage over a scant Republican majority".
The first woman to hold the post, Mrs Pelosi, 82, said nothing in her press release about whether she planned to stay on as minority leader, amid speculation in Washington about her future.
BBC