The Republican National Committee on Friday selected new leaders who were handpicked by former President Donald J. Trump, a move expected to tighten the expected nominee’s hold on the party’s machinery ahead of the general election.

The committee unanimously elected Michael Whatley, who led the North Carolina Republican Party and was the R.N.C.’s general counsel, as its chair and Lara Trump, Mr. Trump’s daughter-in-law, as co-chair.

Both Mr. Whatley and Ms. Trump were endorsed by Mr. Trump last month after Ronna McDaniel, the committee’s leader since 2017, privately told the former president she planned to leave the position. Ms. McDaniel was for months the focus of intense pressure from inside and outside the Trump campaign to step down over the committee’s lackluster fund-raising and criticism over Republicans’ performance in 2022.

Many of Mr. Trump’s allies also criticized Ms. McDaniel, whom Mr. Trump originally picked for the position, for being insufficiently supportive of the former president. They cited her neutrality during the Republican primary and her resistance to his push to call off a series of debates that he refused to participate in.

The new leaders will take the reins of the national party at a critical juncture for Mr. Trump’s campaign, and their elevation is part of his larger effort to effectively merge the R.N.C. with his campaign.

After Mr. Trump dominated the primaries on Super Tuesday, his last remaining rival, Nikki Haley, exited the Republican race, effectively handing him the party’s nomination. Mr. Trump is now focused on the general election, and his campaign is expected to begin raising money in concert with the party, allowing him to raise far larger sums and to tap into the existing party apparatus.