Shirley Bassey: A Very British Diva will trace the Cardiff-born star's rise from poverty to international stardom.
The Irish actress said it was "an absolute honour" to be cast in the role.
The cast also features Lesley Sharp, as Bassey's mother. The one-hour drama is due to be broadcast in the autumn.
Set against the backdrop of mixed-race Britain from the 1930s to the 1960s, the drama tells the story of the singer who was born to a British mother and Nigerian father.
After leaving school at 15 to work in a factory, Bassey was discovered singing in working men's clubs.
She went on to have huge hits including the themes to James Bond films Goldfinger and Diamonds Are Forever.
Co-starring in the drama is The Inbetweeners actor Henry Lloyd-Hughes, who plays Bassey's manager and husband Kenneth Hume.
Executive producer Maxine Watson said: "Dame Shirley Bassey is iconic - she transcends age, race and class.
"Hers is a classic story of overcoming poverty through personal sacrifice and I'm thrilled that we have such a fantastic cast to bring this story to life."
The drama is being shown as part of BBC Two's Mixed Race season.
Source Ruth to me is perfect so I'm happy she is getting more work. And she BETTER be back on Misfits unless I'm done with the show.