William Davis Ardagh (March 21, 1828 – April 16, 1893) was an Ontario lawyer, judge and political figure.

He came to Barrie in Canada West in 1848, articled in law and was called to the bar in 1855.

He entered the practice of law in Toronto with John Willoughby Crawford.

He served as deputy judge in Simcoe County in 1882 and was reeve and later mayor of Barrie.

He moved to Winnipeg, Manitoba, where he served as Deputy Attorney-General and County Court judge.