Cafodd y datganiad ei wneud gan Ysgrifennydd Brexit, David Davis, a phrif drafodwr yr UE, Michel Barnier, yn dilyn trafodaethau cychwynnol ym Mrwsel ddydd Iau.
Dydd Llun oedd y dyddiad gwreiddiol yr oedd trafodaethau i fod i ddechrau, ond roedd amheuon am hynny yn dilyn canlyniad yr etholiad cyffredinol.
Mae'r trafodaethau rhwng y Ceidwadwyr a'r DUP wedi golygu y cafodd Araith y Frenhines ei symud o ddydd Llun i ddydd Mercher yr wythnos nesaf.
Fe wnaeth Theresa May danio Erthygl 50 ym mis Mawrth i ddechrau'r broses o adael yr UE.
Mae disgwyl felly i'r DU adael erbyn Mawrth 2019.
Mae'r pynciau fydd yn cael eu trafod yn cynnwys statws pobl o'r UE sy'n byw yn ym Mhrydain ar hyn o bryd, y costau fyddai'n rhaid i'r DU dalu i adael a sut y bydd y DU yn masnachu gydag Ewrop ar ôl hynny.
Ers yr etholiad yr wythnos diwethaf mae galwadau wedi'u gwneud am safbwynt trawsbleidiol i'r trafodaethau, a dywedodd Prif Weinidog Cymru Carwyn Jones nad oes gan Mrs May fandad ar gyfer Brexit caled bellach.
Ond mae Downing Street wedi mynnu na fydd eu strategaeth yn newid.

Gog the Yorkshire terrier became well known in Leicester because her owner Monti Shortt dresses her in clothes and pushes her around in the buggy.
But the pooch was taken when the owner, who has cancer, quickly popped into the Haymarket Shopping Centre on Friday.
She left Gog in her buggy outside and CCTV shows a woman wheeling it away.
Ms Shortt, 69, said she needs to get her pet back urgently because Gog needs surgery on her knees costing over Â£1,000.
"I haven't been without her since I've had her," said Ms Shortt.
More on this and other stories in Leicestershire
"We come into town regularly and she lights everybody's day up.
"People say they love seeing her and hundreds of people have taken pictures of her."
Gog was wearing a jumper, spotty baby vest and ribbons in her hair when she was stolen.
She is five years old and Ms Shortt has owned her since just before she was seven weeks old.
Ms Shortt uses the buggy to help her carry things and Gog sometimes sits inside.
Leicestershire Police is examining CCTV of the theft, which happened in Humberstone Gate at about 14:50 GMT on Friday.
Ms Shortt's coat, bag and inhalers were also in the stolen buggy but she is only concerned about getting Gog back.
Bydd trafodaethau ffurfiol Brexit yn dechrau ddydd Llun, yn ôl Llywodraeth y DU a'r Undeb Ewropeaidd.
[NEXT_CONCEPT]
A dog that became a local celebrity has been wheeled off in a buggy by a mystery woman, sparking a hunt for the animal's return.