A party needs 218 seats to win control of the 435-member lower chamber of Congress. As of Thursday morning, Republicans were in control of 217 to the Democrats' 206 seats. Results from 10 races were still pending.
The Republican Party was expected to make broad gains in the House during the midterm elections, but Democrat victories in moderate districts blunted the hopes of conservatives.
That has resulted in some Republicans pointing fingers over the party's lacklustre showing. Some have blamed former president Donald Trump, who propped up candidates that backed his debunked claims of fraud in the 2020 election.
But even with a slim majority, House Republicans could derail President Joe Biden's legislative agenda.
Control of the lower chamber would also allow Republicans to launch investigations into Mr Biden's family and administration. The withdrawal from Afghanistan and his son Hunter Biden are both expected to be targets of investigatory panels.
Department of Homeland Security Secretary Alejandro Mayorkas could also be a target as Republicans continue to attack the White House for its handling of the nation's migration crisis.
Some far-right Republicans have even mused about the possibility of impeaching Mr Biden.
In the run-up to the midterm elections last week, Republicans campaigned on the inflation crisis and security on the US southern border.
Any significant legislation passed by the Republican-controlled House faces little chance of being passed in the Senate, where Democrats remain in control, though Mr Biden has said he would be prepared to work with his Republican colleagues.
Republicans select nominee for House speaker
House Minority Leader Kevin McCarthy has received the backing of Republicans to continue as leader, even amid the party's underwhelming performance.
Members voted 188-31 to nominate Mr McCarthy as speaker of the House starting in January, when the Republican Party is expected to take control.
As House minority leader, Mr McCarthy has been the face of Republican opposition to the Democratic agenda and the January 6 committee. He also raised hundreds of millions of dollars during the midterm election cycle.
He faced one challenger, Andy Biggs of Arizona.
A slim majority for either party gives little room for dissent among its members. With the Republican Party divided into different factions of moderate conservatives, Trump loyalists, the Freedom Caucus and others, Mr McCarthy would have to secure near unanimity to pass any legislation.
House Speaker Nancy Pelosi and Democrats experienced the perils of a narrow majority last year, when the Progressive Caucus stalled Mr Biden's social spending and infrastructure bills.
The entire House of Representatives will vote on the next House speaker in January.