Depardieu was caught short on a Paris to Dublin flight and relieved himself on the cabin floor in front of shocked passengers, a witness and the airline said Wednesday.
But a friend of the actor disputed the account, claiming that the 62-year-old bon vivant had been trying to urinate into a bottle and was "mortified" to cause a spillage.
The plane taxied back to the terminal and Depardieu was escorted off the flight by ground crew without incident.
"I will only confirm that he, in effect, urinated in the plane," a Paris spokeswoman for Air France-KLM, parent company of CityJet, operator of the Tuesday flight from Charles de Gaulle that was delayed by the incident.
A passenger told Europe 1 radio Depardieu was visibly inebriated and tried to stand up before take-off, declaring: "I want to piss. I want to piss."
A stewardess asked the well-loved celebrity -- who was on his way to Ireland to play comic book warrior Asterix's huge sidekick Obelix in a film adaptation -- to wait 15 minutes until after the seat-belt lights were put out.
"And there and then he stood up and did it on the floor. We could see he had been drinking. The stewardess was dumbfounded," the witness said.
But friends of the "mortified" star, speaking to AFP on condition of anonymity, said he had told them he was "absolutely not drunk" but had been caught short and forced to pee into a bottle as privately as possible.
They confirmed the witness' account that the stewardess had asked him to wait 15 minutes before the toilets would be opened, and said he had agreed, but added that the flight had then been delayed a further 20 minutes.
A flying companion, fellow actor Edouard Baer, had therefore offered him an empty bottle to ease his aching bladder.
When some urine spilled onto the floor, Depardieu was mortified and offered to clean it up himself, but the crew decided to turn round and taxi back to the terminal and have him escorted off the jet by ground crew, they explained.
"No charges were brought and no fine was imposed, and he had the impression that his position about the misunderstanding and the inflexible attitude of the stewardess had been understood by those he spoke to," one added.
The source added Depardieu had been able take the next flight to Dublin.
"The passenger refused to remain in his seat. It was the captain's decision it was best to return the plane to the stand," a CityJet spokeswoman said, adding the flight was delayed for one hour and 15 minutes.
She said the passenger did not appear to the crew to be drunk. Police were initially called, but he was escorted from the plane by ground crew.
While the spokeswoman attempted to be discreet, refusing to confirm the culprit's identity and speaking only of an "incident on board", her firm CityJet made fun of Depardieu on its public Twitter account.
"As you may have seen on the news, we are busy mopping the floor of one of our planes this morning," the company joked in one message on the popular microblogging site.
Later, it added: "We'd also like to remind all passengers that our planes are fully equipped with toilet facilities."
CityJet said the messages were meant to "poke fun" and "were done this morning in a humorous way. In no way do they reflect an official message."
Depardieu is perhaps the best known face in French cinema, having appeared in almost 200 films, and is best known abroad as the star of the 1990 literary epic "Cyrano de Bergerac" and the US romantic comedy "Green Card".
He is a successful winemaker and restaurateur but in 1990 was convicted of drunk driving. His behaviour has been criticised in the past, notably when he headbutted a press photographer, but he is still a well-loved public figure.