Mortemore appeared as Gertrude in David Glass' production of Gormenghast in 2006/2007. Her film and television appearances include White Heat BBC2/ITV (2012), Ollie Kepler's Expanding Purple World (2010), Salt Grain (2010), Dead Gorgeous, Too Many Cooks, Harry Potter and the Chamber of Secrets as Madame Pince and Wire in the Blood and Daphne & Apollo for the BBC as directed by Clare Kilner.
In 2016 she portrayed a Braavosi woman in the HBO series Game of Thrones in Season 6.
