The former Big Brother star, who has been taking acting lessons for the past few months, will take on the role of Maryisa in Extreme.
The short film follows a group of people receiving therapy for sex addiction and will see Thomas "simulating breathless sex in an aeroplane toilet" in one scene.
According to the Daily Star Sunday, Thomas told a friend: "I'm so excited. After everything that has happened recently I think this could be the start of good things for me.
"The role is quite funny but it's also seductive and flirty, so hopefully I'll be a natural. I've got some life experience under my belt that will stand me in good stead, that's for sure."
Thomas previously made her acting debut in Welsh-language soap Pobol y Cwm (People of the Valley) in 2006, shortly after leaving Big Brother.
Directors are also said to be in talks with Men Behaving Badly actress Caroline Quentin to join Extreme as another sex addict.
Thomas hit the headlines earlier this year when it was revealed that footballer Ryan Giggs had taken out an injunction to prevent their affair being reported in the press.
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