The man's defence lawyer confirmed the plea at Copenhagen City Court as court proceedings over the accident began on Monday morning.
The 25-year-old is accused of negligent manslaughter under aggravating circumstances.
“My client admits that he lost control of the jetski, thereby committing negligent manslaughter,” his defence counsel Jane Ranum said.
The fatal incident, in which the two international students, 18-year-old Leah Bell from Lousiana and 21-year-old Linsey Malia from Massachusetts lost their lives, occurred on May 6th this year near the Langebro bridge in the centre of Copenhagen.
Negligent manslaughter provisions are most commonly used in Denmark in cases relating to road traffic accidents.
Seven other people are also on trial for the lesser charge of putting lives in danger by recklessly driving their jetskis on the busy Copenhagen Harbour.
All seven deny the charges against them.
According to several witness accounts, a number of jetskis were seen travelling at high speeds – estimated by different accounts at between 30-40 and 50-60 kilometres per hour – in the harbour at the time of the accident.
The maximum permitted speed is six knots, around 11 kilometres per hour.
None of the eight individuals had the necessary permits for driving jetskis in the harbour.
The 25-year-old piloted the jetski that crashed into a rented boat near the Langebro bridge, killing the two American women.
There were seven people on board the boat, which was owned by rental company Go Boat.
The seven on board were taking part in a study exchange programme, Study Abroad in Scandinavia (DIS) confirmed at the time of the accident.
A survivor of the accident has previously said that the group became scared after a jetski passed close to them. They had asked Linsey Malia, who was steering the boat, to sail to the side of the harbour just before the accident happened, Ritzau reports.
All eight jetski riders sailed to the harbour in nearby Brøndby after the accident but said they did not realise the seriousness of the incident until police arrived.
The driver of the jetski that crashed with the boat has since been remanded in police custody, partly due to previous convictions for violent behaviour and theft, according to previous reports.
A verdict is expected in the case in January.