The country's parliament impeached Park in December, and she was stripped of her presidential powers pending the court's judgment.
The ruling is expected to be televised live and takes place 11 a.m. (9 p.m. ET).
If the decision to impeach her is upheld, an election for her replacement must be held within 60 days.
Police issued the "Gabho" emergency order in Seoul ahead of Friday's announcement, the highest level possible.
All of police officers are on standby for expected protests, with 270 units being mobilized -- about 21,000 policemen in total.
In downtown Seoul, dozens of police buses line the major Sejong-ro boulevard. Stacks of riot shields are piled outside of the vehicles.
Chaos in South Korean politics
Park's problems began in October, when revelations emerged about the influence Park's confidante and adviser Choi Soon-sil had over the President.
Choi is on trial for meddling in state affairs and extorting money.
Local media and opposition parties have accused Choi of abusing her relationship with the president to force companies to donate millions of dollars to foundations she runs. She denies all charges against her.
Hundreds of thousands of South Koreans braved the brutally cold winter temperatures to take to the streets of Seoul and call for Park's ouster.
In a brief televised apology however, Park made it clear that she had no intentions of resigning. The National Assembly voted soon after 234 to 56 to impeach her.