When she arrived in Congress in 2021, Representative Marjorie Taylor Greene, Republican of Georgia, was quickly stripped of her two committee assignments by Democrats and shunned by her colleagues on Capitol Hill.

Almost three years later, Ms. Greene is poised to hold a gavel for the first time, a sign of the ascendancy of the MAGA wing of the G.O.P. in Congress, where President-elect Donald J. Trump’s most loyal allies will occupy prominent posts next year.

Representative James Comer of Kentucky, chairman of the House Oversight Committee, is planning to create a new subcommittee to partner with Elon Musk and Vivek Ramaswamy to “eliminate government waste.” The committee, which has yet to be created, will work with the new Department of Government Efficiency, known as “DOGE,” and leading Republicans have agreed to allow Ms. Greene to serve as its chairwoman.

Republicans said the committee would be charged with investigating waste and corruption within the federal government.

Even though she is not yet the chairwoman of a committee that does not yet exist, Ms. Greene’s new position appeared to be a done deal, with top Republicans confirming it would be hers to lead when the new Congress convenes in January.