The 19-year-old – who plays Katy Fox in the Channel 4 soap – joined the show in April and featured heavily in the 'Who Pushed Clare?' storyline which saw her character being driven over the edge of a cliff by evil Clare Cunningham (Gemma Bissix).
Her character was also recently involved in a boiler leak plot which subsequently saved a viewer's life.
Speaking of her decision to leave, Hannah – sister to EastEnders' Kara Tointon who plays Dawn Swann – told DS: "I've had such an amazing time at Hollyoaks and I've met so many lovely people.
"It's been brilliant and it's been a really difficult decision to leave. I always said that I'd only do a year and I feel that now is the right time to leave and try something new.
"I'd especially like to thank Bryan Kirkwood and Tony Wood for giving me such great storylines to work on. I'll miss the show and everyone here so much."
Producer Bryan Kirkwood said: "This is a decision which Hannah has come to on her own and I respect her for wanting to move on and try new things.
"She's a lovely young actress who doesn't want to be stuck in one place for too long and I wish her all the very best for the future."
A show source added: "There's quite a big long-running story involving Warren and Louise which bubbles through the early months of next year, so there's a good exit already planned for Katy."
Hannah is due to film her final scenes for the soap in February but will remain on screen until April.