Brazil's Supreme Court has convicted former president Jair Bolsonaro of orchestrating a coup plot following his electoral defeat in 2022, in an unprecedented case against a former Brazilian head of state.

A panel of five Supreme Court justices reached the required majority on September 11 when Justice Cármen Lúcia cast the decisive third vote to convict the 70-year-old right-wing populist. The court found Bolsonaro guilty on all five charges: taking part in an armed criminal organisation, attempting to violently abolish Brazil's democratic order, plotting a coup d'état, and damaging government property and protected cultural assets.

Justice Lúcia described the proceedings as a "meeting between Brazil and its past, its present, and its future," referencing the country's history of democratic upheaval. She stated there was "conclusive evidence" that Bolsonaro led efforts "with the purpose of eroding democracy and institutions."

The conviction stems from events surrounding the 2022 presidential election, when Bolsonaro lost to left-wing candidate Luiz Inácio Lula da Silva. Prosecutors alleged that the coup plot began in 2021 with systematic attempts to undermine public confidence in Brazil's electoral system.

The scheme culminated on January 8, 2023, when thousands of Bolsonaro supporters stormed government buildings in the capital Brasília, just days after Lula's inauguration. The scenes echoed the storming of the US Capitol by supporters of President Donald Trump, a close ideological ally, in January 2021. Demonstrators invaded and vandalised the headquarters of all three branches of government in what prosecutors described as an attempt to incite military intervention against the newly installed president.

According to Estadao, Justice Alexandre de Moraes, the case's rapporteur and a long-time foe of the embattled leader, presented video evidence during the proceedings, including footage of Bolsonaro's inflammatory speech on September 7, 2022, when the former president made threats against Supreme Court justices. Moraes challenged claims by dissenting Justice Luiz Fux that the January 8 events were merely the result of a "disorderly mob."

"I ask: would any of us here allow and affirm that this is freedom of expression, and not a crime, if a mayor, in a small town, inflamed the people against the district judge?" Moraes questioned after showing Bolsonaro's speech.

Only Justice Fux dissented from the majority verdict, acquitting Bolsonaro of all charges after a lengthy 13-hour presentation that criticised both the prosecution's case and the court's jurisdiction.

The final vote rests with Justice Cristiano Zanin, who will announce the trial's outcome. Sentencing is expected on September 12, with Bolsonaro potentially facing more than 40 years in prison.

Bolsonaro, currently under house arrest after being deemed a flight risk, remains a polarising but significant political figure in Brazil. Tens of thousands of his supporters rallied across the country on September 7 in shows of solidarity.

The case has sparked international tensions, particularly with the United States. President Trump has denounced the proceedings as a "witch hunt" and imposed 50% tariffs on various Brazilian goods in response. The Trump administration has also slapped sanctions on Justice Moraes for alleged "serious human rights violations" and announced visa restrictions against court officials.

Lula has condemned Trump's interference as "unacceptable" and an assault on Brazil's sovereignty, accusing the US of having "helped stage a coup."

The conviction represents a watershed moment in Brazilian politics and jurisprudence, as the country grapples with the aftermath of its most serious institutional crisis since the return of democracy in the 1980s.