Yoon on Wednesday became the country's first sitting president to be arrested, in a criminal probe related to his short-lived declaration of martial law on December 3.
Investigators requested a detention warrant on Friday to extend their custody of Yoon for up to 20 days.Â
He has been refusing to talk to investigators and has been held in Seoul Detention Centre since his arrest.
Thousands of protesters have rallied to support impeached South Korean President Yoon Suk-yeol. (AP PHOTO)
"He decided to attend ... to restore his honour by directly explaining the legitimacy of emergency martial law and that insurrection is not established," Yoon's lawyer, Yoon Kab-keun, said in a statement.
TV channels showed a convoy of about a dozen cars and police motorbikes escorting Yoon from the detention centre to the court.
Since police broke up a crowd of Yoon's supporters blocking the gate of Seoul Western District Court in the morning, thousands of supporters gathered after the hearing began at about 2pm (0500 GMT) Saturday in front of a police bus barricade at the court chanting "release the president".
"There are so many supporters of President Yoon Suk-yeol around the court, who still believe in the rule of law and are defending the president," said Lee Se-ban, 30.
Yoon's lawyer said that after the hearing he was expected to return to Seoul Detention Centre to await the court's decision, due on Saturday or Sunday.
Insurrection, the crime alleged against Yoon by the Corruption Investigation Office for High-ranking Officials, is one of the few from which an incumbent South Korean president does not have immunity.
Detention warrant hearings usually last about two hours in South Korea but can last eight to 10 hours if arguments heat up.
