William D. Casey (born February 19, 1945 in Amherst, Nova Scotia) is a Canadian politician.

Casey is currently a member of the Conservative Party of Canada in the Canadian House of Commons. He was first elected, as a member of the Progressive Conservative Party of Canada, to represent the riding of Cumberland—Colchester in the 1988 Canadian election. He lost his seat, along with almost every other PC MP in the 1993 election to Liberal Dianne Brushett. In the 1997 election he retook the seat, defeating Brushett and has represented it since then. In 2004 he moved from the PC party to the new Conservative Party. Casey is a former businessman and stockbroker. He is currently the Deputy Whip of the Official Opposition, and has served as the Progressive Conservative critic of Transport, International Trade, National Revenue, and Foreign Affairs.