While public hearings for Yoon’s impeachment trial could take months, the court is under pressure to decide quickly and bring an end to political uncertainty. Protesters have vowed to keep up their calls for Yoon’s removal during court proceedings.
In the previous two instances a South Korean president faced impeachment, the court reversed one decision and upheld the other.
Observers say what will complicate Yoon’s trial is the fact that the court only has six justices out of nine, as three had retired recently and have yet to be replaced.
If the court upholds impeachment in Yoon’s case, the country must hold fresh presidential elections within 60 days. In the meantime, Prime Minister Han Duck-soo is serving as acting president.
It is unclear if Yoon will take the stand himself during the court hearings.
He ignored a summons to meet prosecutors in Seoul on Sunday, and is set to be ordered in again for questioning. If he fails to come forward this week, police may move to arrest him.
Yoon has defended his decision to impose martial law, and after his impeachment he once again said he would fight until the end.
Minutes after the constitutional court convened on Monday morning, PPP leader Han Dong-hoon announced his resignation.