NASHVILLE — Justin Jones, one of the two Black Democrats expelled from the Tennessee House of the Representatives for leading a gun control protest on the House floor, was sworn back in to his seat on Monday in a swift rebuke to the state’s Republican supermajority.

Within an hour of the Metropolitan Nashville Council unanimously voting to temporarily appoint Mr. Jones back to the seat, the young lawmaker had returned to take his place in the Republican-controlled legislature that overwhelmingly voted to expel him just four days earlier.

After leading hundreds of supporters on a march from the council meeting, Mr. Jones took his oath of office on the steps of the State Capitol, now empowered with a national platform and the backing of Democrats across the state and the country. The moment came two weeks after the mass shooting at a Christian school in Nashville that prompted Mr. Jones and two other Democrats to protest in the House chamber.

“No expulsion, no attempt to silence us will stop us, but it will only galvanize and strengthen our movement,” Mr. Jones said in his first formal remarks.

“Power to the people!” he concluded, and the gallery erupted in cheers.

Nashville’s move to appoint Mr. Jones deepens the bitter rift between the council and the Tennessee legislature’s Republican supermajority, which has flexed its control over liberal-leaning areas and moved to rein in the autonomy of the state’s largest cities. Just hours before the vote, a judicial panel temporarily halted a law that would slash the council in half, after Nashville sued the state.

The council voted 36 to 0 to send Mr. Jones, the only person nominated, back to the House ahead of a special election later this year. The fast pace of his reinstatement meant that he had not missed a single floor session in the House.

In Memphis, the Shelby County Board of Commissioners was set to consider sending Justin J. Pearson, the other expelled lawmaker, back to the legislature on Wednesday.

William Lamberth, the House majority leader, and Jeremy Faison, the chairman of the House Republican caucus, issued a statement ahead of the Nashville council’s vote, saying that “should any expelled member be reappointed, we will welcome them.”

“Like everyone else, they are expected to follow the rules of the House as well as state law,” the two men said.

Mr. Jones and Mr. Pearson will also have the opportunity to run again for their respective seats in the coming months, and both have said that they will do so.

“We witnessed a miscarriage of justice and an egregious assault on our democracy,” said Delishia Porterfield, a councilor who lost to Mr. Jones in the Democratic primary for his state legislature seat, but formally nominated him to return to his seat. As she did so, Ms. Porterfield said the vote would “send a strong message to our state government and across the country that we will not tolerate threats to our democracy.”

The Republican-controlled legislature had taken the rare step of moving to expel Mr. Jones, Mr. Pearson and a third lawmaker, Representative Gloria Johnson, on Thursday, a week after they had marched to the front of the House chamber and interrupted a legislative session by leading protesters in calls for action on gun violence. While it was only the third time since the Civil War era that an expulsion had been carried out, Republicans argued that the breach of House decorum warranted such a step.

President Biden and other high-ranking national officials had voiced their anger at what they viewed as an overly punitive and undemocratic action against two of the chamber’s youngest Black lawmakers. Ms. Johnson, a Knoxville Democrat who narrowly avoided expulsion by one vote, said that she believed race was a factor in the decision to keep her in the body. Republicans have denied that characterization.

“They thought that if they could kick out Representative Justin Jones that he would never again be Representative Justin Jones,” Mr. Pearson told the crowd outside the Capitol. “They were wrong.”

With his fist held high, Mr. Jones was escorted back into the legislature by Ms. Johnson shortly after being sworn in. Mr. Pearson watched overhead from the balcony, as their supporters chanted “Welcome home.”

Lawyers for Mr. Jones and Mr. Pearson — a group that includes Eric H. Holder Jr., the former U.S. attorney general — also warned the legislature on Monday against any further action against them or their districts.

“Any partisan retributive action, such as the discriminatory treatment of elected officials, or threats or actions to withhold funding for government programs, would constitute further unconstitutional action that would require redress,” the lawyers wrote on Monday in a letter to Speaker Cameron Sexton, a Republican.

The decision to expel the two Democrats has further angered hundreds of students, teachers and parents already frustrated with the Republican-controlled legislature’s unwillingness to take up any measure that would restrict access to guns.

Earlier Monday, dozens of people rallied outside the Nashville council meeting, carrying signs that read “No Justin, No Peace,” a riff on the “No justice, no peace” chants that were part of the protest that led the expulsion of the two representatives.

Six red and black ribbons hung on the dais at the front of the room, in honor of the six people killed in the Covenant School shooting last month. A councilor, Zulfat Suara, offered an opening prayer that recognized the Covenant shooting as well as a mass shooting earlier Monday in Kentucky.