Judges unanimously upheld parliament’s decision to impeach Ms Park over her role in a corruption scandal involving her close friend, Choi Soon-sil.
She now loses her presidential immunity and could face criminal charges.
There have been angry scenes outside the court. Police said two protesters had died.
The court ruling is the culmination of months of political turmoil and public protest. An election must now be held within 60 days.
Ms Park’s office said she would not be leaving the Blue House, South Korea’s presidential palace, on Friday nor making any statement.
Acting President Hwang Kyo-ahn has called for calm, saying the government should remain stable to prevent internal conflict from spreading.