A US federal judge has sentenced former far-right Proud Boys leaders Joseph Biggs to 17 years in prison and his co-defendant Zachary Rehl to 15 years.

The pair were sentenced on Thursday (US time), after a jury convicted them of seditious conspiracy for storming the US Capitol in a failed bid to overturn Donald Trump’s 2020 election defeat.

The prison terms handed down by US District Judge Timothy Kelly for Biggs and Rehl were below US sentencing guidelines and far lower than the 33-year and 30-year terms sought by federal prosecutors.

The pair were the first Proud Boys convicted of seditious conspiracy to be sentenced for their roles in the January 6, 2021, attack.

Judge Kelly said he was not “trying to minimise the violence” that occurred, but he noted that the riot was still not on par with a mass casualty event and imposing a stricter sentence could create disparities.

Ahead of his sentencing, Biggs apologised for his actions as he faced Judge Kelly, choking up as he spoke about his daughter. He said she was a sexual assault victim who needed him while he had been locked up.

“I was seduced by the crowd, and I just moved forward. My curiosity got the better of me,” said Biggs.

“I’m not a terrorist. I don’t have hate in my heart.”

Rehl, meanwhile, broke down crying as he read a statement. His lawyer stood next to him, with his hand on Rehl’s back.

“I regret involving myself with any of it,” he said.

Rehl said he had politics consume his life and he “lost track of who and what matters”. He also apologised for letting his family down and asked if Judge Kelly could send him to a federal prison close to his home.

Prosecutors calculated their sentencing recommendation for Rehl, in part, based on evidence he committed perjury when he took the stand in his own defence during the trial and lied about assaulting police with a chemical spray.

“You did spray that officer and you lied about it,” Judge Kelly told him, adding these were “bad facts”.

The attack at the Capitol was meant to stop Congress from certifying Democratic President Joe Biden’s election, which Mr Trump falsely claims was the result of widespread fraud.

“These are very serious crimes,” federal prosecutor Jason McCullough said on Thursday.

“There is a reason why we will hold our collective breaths as we approach future elections. … They pushed this to the edge of a constitutional crisis.”

Mr Trump has a wide lead in the race for the Republican nomination to challenge Mr Biden in 2024.

In one of the debates during his 2020 presidential campaign, Mr Trump famously told the Proud Boys to “stand back and stand by” when he was asked by the moderator to denounce white supremacists.

Two other Proud Boys – Ethan Nordean and Dominic Pezzola – will face sentencing before Judge Kelly on Friday, while the group’s former chairman Enrique Tarrio will be sentenced on September 5.

Prosecutors are seeking a 33-year prison term for Tarrio and a 27-year term for Nordean, both of whom were also convicted of seditious conspiracy.

They are requesting a 20-year term for Pezzola, who was acquitted of seditious conspiracy, but convicted of other serious felonies.

Prosecutors asked Judge Kelly to agree to apply a terrorism enhancement for all five Proud Boys defendants – a move that has the potential to add roughly 15 years to a prison term.

On Thursday, Judge Kelly agreed that Biggs and Rehls’ conduct amounted to an act of terrorism, but he did not apply the enhancement because he said it “overstates the conduct” at issue.

The sentences he imposed, while far lower than what the government requested, still represent among the most stringent to date in connection with the Capitol attack.

To date, former Oath Keepers founder Stewart Rhodes holds the record with an 18-year sentence, after he was convicted of seditious conspiracy earlier this year.

More than 1100 people have been arrested on charges related to the Capitol assault.

-AAP