William Duff Sr. (July 22, 1842[1] – February 18, 1913[2]) was a Scottish-born businessman and politician in Newfoundland.

He represented Carbonear in the Newfoundland House of Assembly from 1889 to 1900.

Duff came to Newfoundland as a clerk for a firm in Harbour Grace.

In 1893, Duff was named governor for the savings bank.

This article about a Newfoundland and Labrador politician is a stub.