William Costello Kennedy, PC (August 27, 1868 – January 17, 1923) was a Canadian politician.

Born in Ottawa, Ontario, he was first elected to the House of Commons of Canada in the riding of Essex North in the 1917 federal election as a Laurier-Liberal. He was re-elected as a Liberal in 1921. From 1921 until his death, he was the Minister of Railways and Canals in the government of William Lyon Mackenzie King.

• "William Costello Kennedy". Dictionary of Canadian Biography (online ed.). University of Toronto Press. 1979–2016.

• William Costello Kennedy – Parliament of Canada biography