Bennie Thompson: The Jan. 6 committee chairman is a veteran lawmaker from a conservative state.

Representative Bennie Thompson, Democrat of Mississippi, wasn’t supposed to be in this position.

After Jan. 6, Mr. Thompson, the chairman of the Homeland Security Committee, negotiated with Representative John Katko of New York, the panel’s top Republican, to create a bipartisan, independent commission to investigate the riot. But when Senate Republicans blocked the move, Speaker Nancy Pelosi turned to a backup plan: forming a special congressional committee to carry out the inquiry.

She turned to Mr. Thompson, 74, a long-tenured member of the Congressional Black Caucus, to lead it.

As the chairman of the nine-member panel, Mr. Thompson has been in charge of approving the committee’s subpoenas, authorizing more than 100 of them. He says an aggressive investigation is needed to properly demonstrate how former President Donald J. Trump sought to misuse federal agencies, such as the Justice Department, to help him stay in power as he spread the lie of a stolen election.

“I’m convinced, and so are the members of our committee, that some of our agencies were positioned to be used to support the Big Lie,” Mr. Thompson said. “We want to show how that positioning occurred, so that the public understands that some of those things in a democracy should never happen.”

Mr. Thompson is the only congressional Democrat from Mississippi, a deeply conservative state. An avid hunter and angler, he has been fending off Republican challenges to Democratic election victories since he got into politics.

At age 21, after he won a seat on the board of aldermen in Bolton, Miss., white residents filed an unsuccessful lawsuit to try to prevent Mr. Thompson and two other Black men from taking their seats on the board.

He will take center stage at the half-dozen Jan. 6 hearings planned for this month, which will lay out the committee’s evidence that aides say will show that Mr. Trump was at the center of a “coordinated, multi-step effort to overturn the results of the 2020 election.”

Mr. Thompson is expected to take the lead on Thursday in questioning the panel’s first two witnesses: a documentary filmmaker, Nick Quested, who was embedded with the right-wing Proud Boys group on Jan. 6, and a Capitol Police officer, Caroline Edwards, who was injured as rioters breached barricades and stormed in.