William Johnston Tupper (June 26, 1862-November 1, 1840) was a politician and office holder in Manitoba, Canada. He served as the province's Lieutenant-Governor from 1934 to 1940.

Tupper was born in Halifax, Nova Scotia, the son of Charles Tupper (who later served as Premier of Nova Scotia from 1863 to 1867, and Prime Minister of Canada in 1896). He was educated at Upper Canada College and Harvard Law School but returned to Nova Scotia to practice law, being called to the bar in 1885. Later in the same year, Tupper enlisted as a private in the Canadian army to assist in putting down the Northwest Rebellion, and remained in Manitoba afterwards. He was called to the Manitoba Bar in 1886, and worked in a Winnipeg law firm with Hugh John Macdonald, son of Prime Minister John A. Macdonald. Tupper also served as President of the Army and Navy Veterans in Canada.

Tupper entered political life in 1914, running as a Conservative in the rural provincial riding of Morden and Rhineland. He lost to incumbent Liberal Valentine Winkler by 1073 votes to 971. Tupper ran against Winkler again in 1915, but lost by a wider margin during a disastrous provincial defeat for his party.

In 1920, Tupper was one of two Conservatives elected to the provincial legislature for Winnipeg, which elected ten members by preferential balloting. He finished second on his party's list, behind John Thomas Haig. Tupper was one of only eight Conservative MLAs in the legislature, and there is no indication that he played a major role in parliament. He ran for re-election in 1922, but finished 21st overall on first-preference votes and was eliminated on the 24th count.

In 1931, Tupper was elected President of the Law Society of Manitoba, holding the position for three years.

Tupper was sworn in as Lt. Governor on December 1, 1934, and served until November 1, 1940. The position was largely ceremonial by this time, and Tupper had little influence over the government of John Bracken. He died in 1947.