Ms Park has been accused of colluding with a friend who allegedly pressured big companies to give money in return for government favours. But if more than three justices rule against impeachment, Park will regain her powers until the next regular presidential election on December 20.
Samsung Group leader Jay Y. Lee has been accused of bribery and embezzlement in connection with the scandal and is in detention.
Election law now requires a snap poll to be held within 60 days. Park had immunity from prosecution while in power. The ani-Park protester in the second photo below holds a signs referencing the eight-member court's unanimous ruling.
Park has become the nation's first impeached president.
Park is the first South Korean president to be removed from office.
The country's Constitutional Court upheld a parliamentary vote to impeach Park over allegations of corruption and cronyism.
Tens of thousands of South Koreans took to the streets of central Seoul on Saturday to celebrate the ousting of President Park Geun-hye. Moon Jae-in, liberal and leader of the Democratic Party, is now ahead in the polls.
Her ouster followed months of political paralysis and turmoil over a corruption scandal that also landed the head of the Samsung conglomerate in jail and facing trial.
31 Oct, 2016: State prosecutors arrest Ms Choi on suspicion of exerting inappropriate influence over state affairs.
Choi is now on trial for abuse of power and fraud. The election day is highly likely to be set on May 9 as there are several public holidays in the first week of May including Buddha's Birthday on May 3 and Children's Day on May 5. Some want the court decision overturned and her case heard again by new judges.
Park's removal would allow South Korean policy makers-including acting President Hwang Kyo-ahn-to focus more on a slowing economy, escalating tensions with North Korea and economic retaliation from China over the Thaad missile-defence system.
1 Jan, 2017: Ms Park denies wrongdoing, calling accusations "fabrication and falsehood". Well, I guess the big question now is how soon prosecutors will summon her for questioning and what kind of punishment she will face if found guilty of the multiple charges against her. Thank you, Ho-jun, for that.
"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.