The eight-part series will also star Sarah Lancashire (Five Daughters), David Hayman (Trial And Retribution), Matthew McNulty (Misfits), Joanna Vanderham (The Runaway) and Emun Elliott (Lip Service, Game Of Thrones) and will be set in England.
Cassidy will play Katherine, a banker's daughter, in the series which will tell the story of a love affair, set against the backdrop of the opening of the first department store.
Filming on the series will begin in Durham, England, next month. The series is written and created by Bill Gallagher. It will be produced by BBC Drama Productions. Executive producer for the BBC is Susan Hogg.