South Korea's ex-president Yoon Suk Yeol has been jailed for life for masterminding an insurrection by trying to impose military rule.

Yoon attempted to subvert the constitution by deploying military troops to seal off the National Assembly and ordering the arrest of politicians on 3 December 2024, a Seoul court ruled. His actions fundamentally damaged South Korea's democracy and deserves a harsh punishment, presiding judge Ji Gwi-yeon told the court.

Prosecutors had sought the death penalty.

Though it was short-lived, Yoon's martial law order left the nation more polarised than ever, and those deep divisions were on full display as the sentencing took place.

Huge crowds of Yoon's supporters gathered outside the court hours before the hearing, holding banners reading "Yoon, again". Many of them broke down in tears following the verdict.

Also present were anti-Yoon protesters, rallying for him to be sentenced to death.

Yoon himself showed no emotion as he learned of his fate. His lawyers alleged that the verdict was not backed by evidence and accused the judge of following a "pre-written script".

If either side launches an appeal, the case will go up to the Supreme Court, which means it could be months before the verdict is finalised.

Yoon shocked his nation on 3 December 2024 by declaring martial law on live television.

He claimed it was to protect the country from "anti-state" forces that sympathised with North Korea, but it soon became clear he was driven by domestic troubles: the opposition which held a parliamentary majority left him a lame duck president, while his wife Kim Keon Hee was at the centre of various corruption allegations.

He rolled back the order within hours, after lawmakers fought their way into the National Assembly to overturn it.

What followed were months of political chaos, Yoon's impeachment, and a string of indictments against him and other top officials.

Former prime minister Han Duck-soo was handed a 23-year jail term last month for his part in the insurrection, while ex-defence minister Kim Yong-hyun, who advised Yoon to impose martial law, was jailed for 30 years on Thursday.

Former interior minister Lee Sang-min, former intelligence commander Roh Sang-won, and ex-police chief Cho Ji-ho were among the other officials jailed for what judges have described as "an insurrection from the top".

Security was tight outside the court on Thursday, with dozens of police buses forming a cordon to restrict public access. Some 1,000 officers were deployed for security operations, local media reported.

Inside the court, judge Ji called Yoon the "insurrectionist leader", although the judging panel found insufficient evidence to rule that he'd planned the martial law order a year before his announcement.

Yoon defended his actions throughout his trial, arguing that as president he had had the authority to declare martial law, sounding the alarm over opposition parties' obstruction of government.

He maintained that the order was necessary "to protect the freedom and sovereignty of the people and to preserve the nation and its constitution".

The ruling Democratic Party, which won the presidential election after Yoon's ouster, accused the court of "undermining judicial justice" by not sentencing Yoon to death.

"[Yoon] masterminded an insurrection that shook the very foundations of our nation," party leader Jung Chung-rae said.

"[Today's decision] is a clear regress from the people's revolution... The public will find it deeply unsatisfactory and unacceptable."

South Korea has not executed anyone on death row since December 1997, so even a death penalty for Yoon would, in effect, be life imprisonment.

Yoon is already serving jail time for abuse of power and obstructing his own arrest after the martial law order. He still faces three more related trials.

Several former presidents before Yoon had also been convicted and jailed, but were pardoned after serving just two to five years in prison – and many expect the same for Yoon.