The former Celebrity Big Brother star plays herself in the scenes recorded last week on the Chatsworth Estate set, The Sun reports.
> Shameless, Life on Mars, The Office: UK shows and their US remakes - pictures
A supposed set insider said: "Imogen was a natural, you'd never know she had never acted before.
"She was really down-to-earth and up for anything. She never complained and she didn't mind sending herself up."
Last November it was reported that Thomas will play the part of sex addict Maryisa in upcoming movie Extreme.
Thomas has previously appeared in E4's Dead Set and the Welsh S4C soap Pobol y Cwm.
Shameless returns to Channel 4 for the second part of its ninth series later this year.
> Imogen Thomas to star in The Bachelorette
Watch the Shameless series nine trailer below