At the height of Speaker Kevin McCarthy’s quest for his post in January, Representative Chip Roy, Republican of Texas, darted from meeting to meeting ensuring that hard-line conservatives got what they wanted before agreeing to back the California Republican.

One by one, nearly all of their demands were met in what Mr. Roy would later call a “power-sharing” agreement between Mr. McCarthy and his right flank. The hard right won three seats on the influential House Rules Committee (one went to Mr. Roy); a commitment from Mr. McCarthy that Republicans would never raise the debt ceiling without deep spending cuts; and a rule allowing any one lawmaker to force a vote to oust the speaker should he fail to keep his promises.

Now, Mr. Roy, 50, the policy chairman of the ultraconservative House Freedom Caucus who has emerged as the hard right’s spending expert, is accusing Mr. McCarthy of having reneged on the deal, and is attempting to exert his leverage again — this time with potentially dire consequences. He and his allies are attempting to shoot down the agreement Mr. McCarthy reached with President Biden to suspend the debt ceiling just days before the country is headed for default.

If not, he said, the House Freedom Caucus might once again have to go toe-to-toe with Mr. McCarthy. Several members have floated the idea of calling for Mr. McCarthy’s removal.

“If we can’t kill it, we’re going to have to regroup and figure out the whole leadership arrangement again,” Mr. Roy said Tuesday on Glenn Beck’s radio show.

That’s a far cry from the position Mr. Roy found himself in only weeks ago, when he worked alongside House G.O.P. leaders to ensure passage of a far more conservative debt-limit bill, which would have lifted the borrowing limit only in exchange for substantial spending cuts. Representative Garret Graves, Republican of Louisiana and an ally of Mr. McCarthy’s, said he gained respect for Mr. Roy working tightly with him on that package.

“I didn’t have an incredibly high opinion of Representative Chip Roy going into it. He’s one of my best friends now,” Mr. Graves said.

Now, Mr. Roy, who is a mix of legislative wonk and speechifying firebrand, has been circulating documents breaking down all the different ways he believes Mr. McCarthy’s 99-page debt limit deal is, in his words, a “betrayal” of conservatives. In an easy-to-digest format, they lay out — step by step — how the agreement Mr. McCarthy reached with Mr. Biden falls short of conservative demands to rein in spending, streamline energy project permitting and impose stringent work requirements for social safety net benefits.

He and his allies view the country’s $31.5 trillion national debt as a greater threat to America than the Treasury Department’s warning that the country could default on certain bills by June 5.

“Not one Republican should vote for this deal,” Mr. Roy said at a Freedom Caucus news conference on Tuesday, a few hours before he broke with his party to try to block the measure from the floor in a vote in the House Rules Committee. The effort failed; only one other Republican joined him in opposing a measure to advance the deal to a floor vote on Wednesday.

Still, the “no” votes against the legislation are beginning to pile up. By Tuesday afternoon, more than 30 House Republicans had gone on record against it.

“Bill’s horrible for America,” said Representative Clay Higgins, Republican of Louisiana.

Mr. McCarthy and his leadership team have been working hard to shore up support, distributing their own charts and graphs touting reduced spending. The bill appeared on track to pass on Wednesday, with a substantial number of Democratic votes to compensate for G.O.P. defections.

But Mr. Roy’s charts are fueling the arguments of other conservatives as they fight the legislation. He distributed a four-page memo last month of talking points for other Republicans as the negotiations went on. Then he posted two charts emphasizing what he called the failings of the deal.

Mr. Roy “provides the most concise summary I’ve seen regarding the problems with the debt-ceiling deal,” Senator Mike Lee, Republican of Utah, who has pledged to delay a Senate vote on the bill, wrote on Twitter.

Born in Bethesda, Md., Mr. Roy grew up in the Washington area. His father worked for the I.R.S., and he got his law degree from the University of Virginia (the football players Tiki and Ronde Barber, whom he befriended there, attended his wedding). But he learned hardball politics in Texas. He served as Senator Ted Cruz’s chief of staff and in many ways mirrors his former boss’s pugnacious and verbose style.

But unlike many in the Freedom Caucus, he is no acolyte of former President Donald J. Trump. He voted to certify Mr. Biden’s victory and has endorsed Florida Governor Ron DeSantis for president.

Mr. Roy likes to invoke a scene from the movie “Braveheart” when describing what conservatives’ approach should be to the debt limit. It’s the one where Scottish freedom fighters have formed a tight line and their leader, William Wallace, repeatedly orders, “Hold!” before they launch a unified spear attack against the British.

“My position is: Hold the damn line,” he says.

Mr. Roy has claimed that one of Mr. McCarthy’s concessions to the hard right was a pledge that nothing would pass out of the Rules Committee without the support of all nine Republicans on the panel. On Tuesday, Republicans split over the debt ceiling package, which advanced to the floor by a vote of 7 to 6, with Mr. Roy and Representative Ralph Norman, Republican of South Carolina, joining Democrats in voting against the measure.

Mr. Roy has repeatedly said he feels betrayed by Mr. McCarthy.

“I think this is going to be a problem for him,” Representative Ken Buck, Republican of Colorado, said of Mr. McCarthy’s push to pass the debt ceiling deal. “They’re hemorrhaging.”

He said he believed a move to oust Mr. McCarthy could be in the works if the speaker advances the bill without a majority of Republicans. Mr. Buck said he could see the number of Republicans opposing the bill rising to more than 100 as lawmakers learned more about its contents.

Democrats see Mr. Roy’s tactics as putting the country at risk.

“This represents an all-time high in recklessness and stupidity,” Representative Jim McGovern, Democrat of Massachusetts, said of Republican efforts to use the debt ceiling as leverage. He added: “Democrats have had to be the adults in the room.”