Walker landed the title role in the television series "Lorna Doone" before making her feature debut in "Shogun Mayeda" (aka "Journey of Honor") (1991). In that same year she appeared in "Les Equilibristes" and in Mike Newell's "Enchanted April", in which she played an aristocrat eager to escape the attentions of her persistent male admirers. Walker first gained international attention in 1992 as a single-minded English member of an Irish terrorist group in Phillip Noyce's "Patriot Games". In 2003 she had a starring role in the BBC drama series "State of Play".