Sewell, 47, will play Lord Melbourne, the long-running Queen Victoria's first prime minister.
"The two immediately connected and their intimate friendship became a popular source of gossip that threatened to destabilize the government -- angering both Tory and Whigs alike," press notes said of Sewell's prime minister and Coleman's monarch.
The program's ensemble will also include Paul Rhys, Peter Firth, Catherine Flemming, Eve Myles, Nigel Lindsay and Adrian Schiller. The program was created and written by novelist Daisy Goodwin, who is making her screenwriting debut.
Filming is to begin this month in the northern part of England.
Sewell has appeared in the films Hercules, Abraham Lincoln: Vampire Hunter and A Knight's Tale. His TV credits include Parade's End, The Pillars of the Earth and the upcoming The Man in the High Castle.