Mr Yoon’s political future hangs in the balance, with the country at odds over whether or not he should be thrown out of office for good.
The 64-year-old shocked MPs, the public and international allies in early December when he declared martial law, meaning all existing laws regarding civilians were suspended in place of military law.
It was only short-lived, as mass protests erupted and politicians on both sides voted to make Mr Yoon’s declaration void in a matter of hours.
His presidential powers were suspended when the opposition-dominated assembly voted to impeach him on 14 December, accusing him of rebellion.
The vote on Thursday night – Friday morning UK time – is on whether to dismiss or reinstate the president, who will still face criminal charges irrespective of the outcome.
Here we look at the man behind South Korea‘s political crisis – and his career to date.
Prosecuted his own predecessors
Yoon Suk Yeol was born in 1960 during the military dictatorship of the Second Republic of Korea.
His father was an emeritus professor of economics and his mother was a lecturer at a women’s university before giving up her job to marry his father.
He was exempted from national service due to a condition called anisometropia, which results in blurred and unequal vision.
Mr Yoon studied law and began work as a junior prosecutor after graduating. Following the Gwangju Uprising of 1980 he and his colleagues held a mock trial, in which he played the prosecutor that sentenced the president to death. Fearing for his safety, he fled to Gangwon Province – one of three in South Korea that have a special self-governing status.
He was appointed prosecutor-general by his liberal predecessor, President Moon Jae In, in 2019 – but their relationship broke down when Mr Yoon launched an investigation into one of his key ministers – making headlines across the country.
Mr Yoon was later involved in the prosecutions of former presidents – Park Geun Hye who was impeached and convicted for corruption – and Lee Myung Bak, jailed for bribery, embezzlement, and tax evasion.
When Mr Moon’s single five-year term ended in 2022, Mr Yoon announced his candidacy to be his replacement – despite no prior political experience. He only won by 0.73% of the vote.
Anti-Korean unification and US charm offensive
Being part of the People Power Party – on the other side of the political spectrum to his predecessor – Mr Yoon’s policies and style of government have been vastly different.
While Mr Moon was warmer towards North Korea, with the ultimate view of friendly unification, Mr Yoon soon proved hostile – deciding instead to strengthen ties with the United States and Japan.
Joint military exercises with both countries were stepped up – and the president went on a charm offensive with their leaders.
During a state visit to the US in 2023, Mr Yoon astounded guests by serenading then-president Joe Biden with the song American Pie.
Several months ago, his office said he had taken up golf lessons again for the first time in eight years in anticipation of Donald Trump returning to office and in light of his love of the sport.
He was the first South Korean leader to attend a NATO meeting when he visited leaders in Madrid in 2022 and has provided significant military and financial aid to Ukraine.
Struggled to pass legislation
Domestically, however, he quickly proved unpopular.
After he was elected, he made a point of greeting journalists personally as he arrived at work. But as time has gone on, police have carried out an increasing number of raids on the homes and newsrooms of journalists critical of his leadership, who he describes as “fake news”.
With a parliament dominated by the opposition Democratic Party, he has struggled to pass legislation, with only 29% of his bills until January going through.
He has instead relied on the use of the presidential veto, which he has employed more than any of his predecessors since the end of military rule in 1987.
Initially, he battled to get his cabinet ministers in post – with four withdrawing from the process over the parliamentary backlash.
He also wanted to transfer his office – from the famous Blue House palace in central Seoul to a defence ministry building elsewhere – but the plans sparked controversy over their huge cost.
His unpopularity was reflected in April’s parliamentary elections – which saw the opposition party re-take the majority.
Wife embroiled in multiple scandals
Beyond his policies, Mr Yoon has faced several scandals.
Many have involved his wife, Kim Keon Hee, who opted for the title ‘First Spouse’ instead of ‘First Lady’.
Late last year spy camera footage was published showing Ms Kim accepting a £1,730 Dior handbag as a gift. When the news broke, it plunged her husband’s party into turmoil and was widely referred to during the parliamentary election campaign.
Mr Yoon apologised on her behalf and said she should have conducted herself better. Recently he apologised on national TV and declared he was setting up an office to oversee her duties.
Ms Kim is also accused of being involved in stock price manipulation before her husband was elected.
Together, the couple have faced calls for an investigation into an alleged inappropriate relationship between them and a polling company, which they have vehemently denied.
This year Mr Yoon vetoed a bill calling for a special prosecutor investigation into the death of a South Korean marine in 2023, which led to suspicions of a cover-up.
Introducing martial law
In his most controversial move, Mr Yoon introduced martial law on 3 December 2024, giving the military commander unlimited authority to make and enforce laws.
Mr Yoon told the nation that martial law was needed to defend the country from nuclear-armed North Korea and pro-North anti-state forces, and to protect its free constitutional order, although he cited no specific threats.
But security and defence analyst Professor Michael Clarke told Sky News he believed the introduction of martial law was simply Mr Yoon’s attempt to thwart his political opponents.
The move came after two years of Mr Yoon struggling to push his agenda through in an opposition-controlled parliament.
His conservative People Power Party has been in a deadlock with the liberal Democratic Party over the upcoming budget bill, and he had also dismissed calls for independent investigations into scandals involving his wife and top officials, drawing criticism from his political rivals.
Opposition leader Lee Jae-myung said the declaration of martial law was “unconstitutional” and called for the public to protest outside parliament in South Korean capital, Seoul, and even some members of the president’s own party spoke out against him.
Mr Yoon had ordered in his declaration that all political party and parliamentary activities cease, but MPs still headed to parliament to vote on the martial law ruling.
As clashes continued outside, MPs voted to block the declaration.
President refused to be detained
An arrest warrant was issued for Mr Yoon on 31 December, as a joint investigation involving police and military authorities began looking at his power grab to see whether it amounted to an attempted rebellion.
But Mr Yoon’s presidential security service prevented dozens of investigators from arresting him after a standoff lasted nearly six hours on 3 January.
The country’s anti-corruption agency said it withdrew its investigators after they were blocked from entering Mr Yoon’s official residence due to concerns about the safety of its members.
The agency expressed “serious regret about the attitude of the suspect, who did not respond to a process by law”.
He was finally arrested 12 days later, when police returned with 3,200 officers to detain him.
A motorcade of black SUVs was seen leaving the gates of his hillside residence, where he had been holed up for weeks behind barbed wire and a small army of personal security.
Mr Yoon said the “rule of law has completely collapsed” in a video message recorded before he was escorted to the headquarters of an anti-corruption agency.
He said he was complying with the detention warrant to prevent clashes between police and the presidential security service.
