Depardieu, 76, is accused of having groped a 54-year-old set dresser and a 34-year-old assistant director during filming in 2021 of Les Volets Verts ("The Green Shutters").
The actor faces up to five years in prison and a fine of 75,000 euros ($A128,920) if convicted.
Depardieu denies any wrongdoing.
To reporters outside the courtroom on Monday, he said "I'm okay".
Inside, he told the judges that he was prepared to answer the court's questions.
"We will be able to show in an impartial, objective and incontestable manner that all of the accusations are lies," his lawyer, Jérémie Assous, told journalists.
"The truth will be obvious and the truth is on our side," he said.
Depardieu's long and storied career has turned the trial into a post- #MeToo test of the willingness of France and its movie industry to confront sexual violence and hold influential men accountable.
Depardieu has been a darling of French cinemagoers but his alleged boorish behaviour off-screen has also made headlines.
He has been accused publicly or in formal complaints of misconduct by more than 20 women, but so far only the sexual assault case has proceeded to court.
Feminist and historian Florence Montreynaud joined other campaigners demonstrating outside the court.
Prosecutors say Depardieu trapped the set dresser with his legs before groping her waist and breasts in front of witnesses. She says the actor also used obscene language and had to be pulled away by bodyguards.
The assistant director alleged that Depardieu groped her both on set and in the street.
Depardieu grasped his lawyer's shoulder as he strode calmly into the courtroom but didn't testify on Monday.
Instead, his lawyer sought to cast doubt on witness testimony and said police acted under instructions from magistrates who led the investigation to "make Depardieu fall".
Depardieu listened intently, sometimes nodding.
The plaintiffs' lawyers said they would lay out their evidence later.
One of the lawyers, Carine Durrieu Diebolt, said Depardieu had apologised to her client at the time. "So why apologise if you haven't done anything?"
Durrieu Diebolt had previously said that four additional women who say they have been sexually assaulted by Depardieu would testify.
with Reuters
