By including Enrique Tarrio, the former leader of the Proud Boys, in his extraordinary pardons for the events of Jan. 6, 2021, President Trump granted clemency on Monday to a man whom prosecutors have described as a savvy, street-fighting extremist who helped his compatriots in “Trump’s army” initiate an assault on the Capitol.

Mr. Tarrio, 42, was serving a 22-year prison term after being convicted of seditious conspiracy and other felonies for his role in the Capitol attack. His was the longest sentence handed down against any of the nearly 1,600 people charged in connection with Jan. 6.

A representative for Mr. Tarrio said he had been released from a federal prison in Louisiana and was expected to return to Miami, his hometown, on Tuesday afternoon.

Even before Jan. 6, Mr. Tarrio was among the best-known far-right figures in the country, having been involved in violent protests going back to the deadly neo-Nazi rally in Charlottesville, Va., in August 2017. Rarely seen without his sunglasses and baseball cap, he took control of the Proud Boys the next year after the group’s founder, Gavin McInnes, stepped aside.

But Mr. Tarrio is arguably better known for the part he played in supporting Mr. Trump during the 2020 election — and in the chaotic months after he lost the race. The Proud Boys were thrust into the heart of that campaign two months before Election Day when Mr. Trump, at one of the presidential debates, called out the group by name, telling its members to “stand back and stand by.”

Mr. Tarrio responded immediately on social media, “Standing by, sir.”

In December of that year, Mr. Tarrio responded to a message that Mr. Trump himself posted on social media, summoning his supporters to Washington on Jan. 6 for what he said would be a “wild” protest. The day after, Mr. Tarrio established a crew of “hand-selected members” for the rally, court papers said, known within the Proud Boys as the Ministry of Self-Defense.

During the trial of Mr. Tarrio and four other Proud Boys, federal prosecutors described how the group under his control was “thirsting for violence and organizing for action” after Mr. Trump lost the election and ultimately fought at the Capitol “to keep their preferred leader in power no matter what the law or the courts had to say about it.”

Mr. Tarrio was not in Washington on Jan. 6. He had been kicked out of the city days earlier by a local judge presiding over separate criminal charges brought against him for vandalizing a Black church after an earlier pro-Trump rally. But prosecutors say that he and other members of his group frenetically exchanged text messages while the mob, with the Proud Boys in the lead, overran the Capitol.

Ultimately, video clips of the attack showed that the Proud Boys were instrumental in encouraging other rioters to confront the police or in confronting officers themselves. Members of the group took part in several breaches of police lines and were at the forefront of violence almost the entire day.

When he was sentenced in Federal District Court in Washington, Mr. Tarrio sought to portray himself as humbled by the events of Jan. 6, apologizing for his role in the riot and calling it a “national embarrassment.”

“I am not a political zealot,” he said.

A few months before he went on trial, he met secretly with federal prosecutors who, by his own account, offered him leniency if he could corroborate their theory that he had been in touch with Mr. Trump in the run-up to Jan. 6 through at least three intermediaries.

Mr. Tarrio said he told the prosecutors they were wrong — a position that, regardless of its veracity, would have surely pleased Mr. Trump when it was made public.

It remains unclear what Mr. Tarrio’s release might mean for the future of the Proud Boys. He is a polarizing figure in the group, beloved by some members and despised and distrusted by others, including many from Miami, his hometown.

Moreover, the organization dismantled its national leadership and largely retreated from high-profile demonstrations after Jan. 6, which led to the arrest and prosecution of dozens of its members. While some chapters of the Proud Boys used violent language on their online accounts during the 2024 campaign, the group was barely present on the street or at rallies in support of Mr. Trump.