More than 6000 police officers, including anti-riot squads, were deployed to secure the Senate, where about 400 anti-Duterte demonstrators converged on Monday chanting "Convict Sara now".
Duterte did not appear but was represented by her lawyers at the start of the trial, which will run for about three months.
If convicted of the charges, which include amassing unexplained wealth and publicly threatening to have Marcos assassinated, Duterte may be permanently disqualified from holding public office. She denies the charges.
Representative Gerville Luistro, who leads the prosecution team, said there was adequate evidence and witness accounts to convict the vice president.
"This is the moment when the republic must demonstrate that laws are applied equally to the powerful and the powerless alike," Luistro said.
Sheila Sison, head of the vice-president's legal defence, expressed doubt whether prosecutors have legitimate evidence to back up their allegations against Duterte, who rose to power with a landslide electoral victory.
"This court, and we as a people, must guarantee that all efforts to hold our leaders accountable must be done right," Sison said.
"Impeachment should never be abused."
A conviction would be a lethal blow to the vice-president's announced plan to seek the presidency in mid-2028, when Marcos ends his six-year term.
They were running mates in the 2022 elections in a whirlwind alliance that combined the vote-getting power of two of the country's most formidable political dynasties, but the union rapidly fell apart.
The vice-president is the daughter of former President Rodrigo Duterte, Marcos' predecessor.
He was arrested in 2025 on orders of the International Criminal Court and flown to The Hague, where he is detained and is scheduled to face trial over alleged crimes against humanity on November 30.
The charges stem from the ex-president's brutal anti-drugs crackdowns that left thousands of mostly poor suspects dead, alarming Western governments and human rights groups. Rodrigo Duterte has denied authorising extrajudicial killings but repeatedly threatened suspects with death while in office.
The vice-president has blamed Marcos for her 81-year-old father's arrest and handover to the ICC.
In June, the House of Representatives, which is dominated by Marcos' allies, voted overwhelmingly to impeach the vice-president over alleged unexplained wealth, misuse of confidential state funds and a public threat to have the president, his wife and a former House speaker and ally assassinated if she herself were killed due to their political disputes.
Sara Duterte has generally denied the charges but has refused to publicly answer the allegations in detail before the impeachment trial.
Her supporters have accused Marcos and his key aides of politically persecuting the vice-president and her senatorial allies to ensure her impeachment.
Two-thirds of the 24-member Senate, or 16 votes, are needed to convict the vice-president.
