If the court unseats Park, the country's election law requires a presidential vote within 60 days, which likely means May 9.
The ruling would instantly strip Park of her powers and also her immunity against prosecution. She could be interrogated by prosecutors seeking to indict her on criminal charges. Park has repeatedly refused to be interviewed by prosecutors over the scandal in past months, but that will be harder to do if prosecutors have an arrest warrant.
If a presidential election is triggered, opinion polls favor liberal opposition politician Moon Jae-in, who lost the 2012 race to Park, to succeed her.
A Moon presidency could bring significant changes after a decade of conservative rule. He stresses the need for dialogue with belligerent, nuclear-armed North Korea, which would be a dramatic departure from Park's hard line.
Moon also vows to "reconsider" the South's plans to deploy this year an advanced U.S. anti-missile system; China says the system's powerful radar is a security threat.