The pop star, 36, will appear in the BBC1 soap for a stint later this year as part of the Taylor family who recently moved to Albert Square.
She will play single mum Karen Taylor’s younger sister Kandice, and is rumoured to be just as outspoken as the rest of the brood.
Hannah is another fresh signing for show chief John Yorke since he took over from Sean O’Connor, who quit in June and comes just a day after he announced Tamzin Outhwaite’s return.
Revealing her excitement about joining the cast Hannah said: “I’m over the moon to be joining the show, it’s such a huge part of British telly. I’m really looking forward to getting started and I can’t wait to see the Square in the flesh. Walford here I come.”
Hannah has a strong acting background having starred in the BBC1 series Primeval as Abby for three years, and winning parts in Casualty and Death In Paradise.
A TV source said: “Producers are excited about casting Hannah in the show and if she proves popular she could be back as a more permanent fixture.”
Hannah is the latest in a long list of singers to appear on soaps, including Blue’s Lee Ryan, McBusted’s Matt Willis, Girls Aloud’s Sarah Harding, Boyzone’s Keith Duffy, Shayne Ward and Kym Marsh.