Jacob Chansley, the former actor and Navy sailor better known as the QAnon Shaman, who was portrayed by a prosecutor as “the flag-bearer” of the Jan. 6 attack on the Capitol, was sentenced on Wednesday to 41 months in prison.

Mr. Chansley, 34, emerged as one of the riot’s most familiar figures, largely because of the outlandish costume he wore that day: a horned helmet, a fur pelt draped across his naked shoulders and a thick patina of red-white-and-blue face paint.

Images of him standing on the Senate floor hollering and brandishing a spear made from a flagpole shot around the world, a stark reminder of the role played in the assault by adherents of QAnon, the cultlike conspiracy theory embraced by some backers of former President Donald J. Trump.

Mr. Chansley’s sentence, handed down by Judge Royce C. Lamberth of Federal District Court in Washington, brought an end not only to one of the most widely publicized Capitol cases, but also to one of the strangest. Not long after the attack, Mr. Chansley’s lawyer, Albert Watkins, announced that his client wanted Mr. Trump to pardon him and later offered to have him testify at the former president’s second impeachment trial.

In February, Mr. Watkins persuaded a federal judge to order the jail in Virginia where Mr. Chansley has been detained for most of his case to serve a strict diet of organic meals. The next month, Mr. Chansley gave a widely watched interview to “60 Minutes,” saying that his actions on Jan. 6 were not an assault on the nation, but rather a way to “bring God back into the Senate.”

This circuslike atmosphere continued on Wednesday as scores of people attended a court hearing where Mr. Watkins asked Judge Lamberth to heal the country’s divisions by issuing a fair sentence. Mr. Watkins told the judge that he could “mete out justice and emphasize common ground upon which all of us can somehow bridge this great divide.”

When Mr. Chansley addressed the court, he quoted Jesus, Gandhi and Justice Clarence Thomas. He went on to discuss his tattoos, his late grandfather’s role in his life and the prison movie “The Shawshank Redemption.”

He also apologized for his role in attacking the Capitol, saying that in the days since, he has often looked into the mirror and told himself, “You really messed up, royally.”

More than 30 people have been sentenced in connection with the Capitol attack, most of whom have avoided prison time by pleading guilty to minor crimes like disorderly conduct or illegally parading in the building. Last week, a former New Jersey gym owner was also given 41 months in prison for punching a police officer during the riot — the first of almost 200 riot cases of people charged with assault to reach the sentencing phase.

Mr. Chansley pleaded guilty in September to a single felony count of obstructing an official proceeding before Congress. In court on Wednesday, Mr. Watkins argued for leniency on his behalf saying, among other things, that he had lived for several years with mental illness. After an evaluation, Judge Lamberth found Mr. Chansley competent enough to proceed with his case.

The government had recommended that he be sentenced to 51 months in prison, saying that long before Jan. 6, Mr. Chansley encouraged his large social media following to “identify traitors in our government” and to “stop the steal” — a reference to Mr. Trump’s repeated lies that the 2020 election was marred by fraud.

Two weeks after the presidential race ended, Mr. Chansley was already promoting violence online, prosecutors say, posting a message that read, “We shall have no real hope to survive the enemies arrayed against us until we hang the traitors lurking among us.”

On Jan. 6, the government says, Mr. Chansley was among the first 30 rioters to enter the Capitol and quickly used a bullhorn to “rile up the crowd and demand that lawmakers be brought out.” Within an hour, he had made it to the Senate floor, taking the seat that Vice President Mike Pence had only just evacuated and leaving a note on the dais saying, “It’s Only A Matter of Time. Justice Is Coming!”

In the days after the attack, Mr. Chansley gave an interview to NBC News in which he said he considered Jan. 6 “a win.” He also told the F.B.I. that he believed Mr. Pence was “a child trafficking traitor” and that the U.S. government was tyrannical, prosecutors say.

After Mr. Chansley’s lengthy speech to the court, Judge Lamberth thanked him, saying the comments were among the most remarkable he had heard in 34 years on the bench. But the judge then told Mr. Chansley that he would still have to serve time in prison.

“What you did is terrible,” he said.