"The negative effects of the president's actions and their repercussions are grave, and the benefits to defending the constitution by removing her from office are overwhelmingly large", acting chief justice Lee Jung-mi said in a 20-minute ruling broadcast live on national television. "It's very clear that former president Park operated out of the boundaries of the Korean Constitution", said political scientist Kim Jae Chun from Sogang University.
A presidential election will be held within the next 60 days.
Park also now has the dubious distinction of being the nation's first democratically elected leader to be expelled from the Blue House.
She is accused of colluding with a friend into forcing big business to donate millions of euros into return for policy favours.
Oct 31, 2016: State prosecutors arrest Choi on suspicion of exerting inappropriate influence over state affairs. His trial began on Thursday.
Jan 1, 2017: Park denies wrongdoing, calling accusations "fabrication and falsehood".
Police are on high alert for the day of the ruling in case protesters supporting or opposing Park clash or otherwise react violently to the decision. "Justices who reject the motion would face fierce criticism and public ire, and they know that", said Scott Seaman, Asia director at Eurasia Group, in a recent note.
"The biggest problem is that the far-right faction, including Park, is already provoking a mass protest", Woo added. She could be interrogated by prosecutors seeking to indict her on criminal charges.
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People on both sides have threatened not to accept a Constitutional Court decision.
If Hwang resigns as acting president, the position will be filled by Yoo Il-ho, deputy prime minister and minister of strategy and finance.
USA and South Korean marines participate in the endurance exercise in temperature below minus 20 degrees celsius under a scenario to defend the country from any possible attacks from North Korea.
You might have heard a thing or two about Park, South Korea's now former president.
China has vociferously protested against the deployment, fearing its sophisticated radar could see into its own missile deployments.
Park will still get bodyguards, according to the law.
After South Korea's last presidential impeachment, of liberal President Roh Moo-hyun in 2004, the court reinstated him after two months, saying allegations of minor election law violations and incompetence weren't enough to justify his removal.