Former Brazilian President Jair Bolsonaro was sentenced on Thursday to 27 years and three months in prison hours after being convicted of plotting a coup to remain in power after losing the 2022 election, dealing a powerful rebuke to one of the world's most prominent far-right populist leaders.

The conviction ruling by a panel of five justices on Brazil's Supreme Court, who also agreed on the sentence, made the 70-year-old Bolsonaro the first former president in the country's history to be convicted for attacking democracy, and drew disapproval from the Trump administration.

"This criminal case is almost a meeting between Brazil and its past, its present and its future," Justice Carmen Lucia said before her vote to convict Bolsonaro, referring to a history checkered with military coups and attempts to overthrow democracy.

There was ample evidence that Bolsonaro, who is currently under house arrest, acted "with the purpose of eroding democracy and institutions," she added.

Four of the five judges voted to convict the former president of five crimes: taking part in an armed criminal organisation; attempting to violently abolish democracy; organising a coup; and damaging government property and protected cultural assets.

The conviction of Bolsonaro, a former army captain who never hid his admiration for the military dictatorship that killed hundreds of Brazilians between 1964 and 1985, follows legal condemnations for other far-right leaders this year, including France's Marine Le Pen and the Philippines' Rodrigo Duterte.

Bolsonaro's close ally US President Donald Trump had called the case a "witch hunt" and in retaliation hit Brazil with tariff hikes, sanctions against the presiding judge, and the revocation of visas for most of the high court justices.

Asked about the conviction on Thursday, Trump again praised Bolsonaro, calling the verdict "a terrible thing."

"I think it's very bad for Brazil," he added.

As he watched his father's conviction from the US, Brazilian Congressman Eduardo Bolsonaro told Reuters he expected Trump to consider imposing further sanctions on Brazil and its high court justices.

US Secretary of State Marco Rubio said on X the court had "unjustly ruled," adding: "The United States will respond accordingly to this witch hunt."

The verdict was not unanimous, with Justice Luiz Fux on Wednesday breaking with his peers by acquitting the former president of all charges and questioning the court's jurisdiction.

That single vote could open a path to challenges to the ruling, which could push the trial's conclusion closer to the October 2026 presidential election.

Bolsonaro has repeatedly said he will be a candidate in that election despite being barred from running for office.

The Supreme Court also ruled to convict seven of Bolsonaro's allies, including five military officers.

The verdict marks the first time since Brazil became a republic almost 140 years ago that military officials have been punished for attempting to overthrow democracy. (Reuters)