Fred Thomas Dubois (May 29, 1851 – February 14, 1930) was an American politician from Idaho who served two terms in the United States Senate.

He launched a successful campaign to disenfranchise Mormon voters in the territory on the grounds they broke the law by practicing polygamy.

Dubois strongly supported Idaho's application for statehood and opposed efforts to split the territory among neighboring regions.

[7] Idaho became a state in July 1890 and that November, Dubois helped engineer a plan for the Idaho Legislature to effectively elect three people to the U.S. Senate: Governor George Shoup to the Class 2 seat up for election in 1894, state constitutional convention member William J. McConnell to serve for the remainder of the 51st Congress, ending in March 1891, and Dubois himself to succeed McConnell and serve a full six-year term in the Class 3 seat beginning in March 1891.

During his first term in the Senate, Dubois concentrated on domestic politics, advocating for positions that he thought would benefit Idaho.

But in 1900, after refusing to rejoin the Republican Party, he was elected again to the United States Senate by the Democratic Idaho Legislature by defeating Shoup, his onetime political ally.

[10] During his second term in the Senate, Dubois continued to advocate abandoning the gold standard, but focused most of his attention on opposition to imperialism and Mormonism.

Dubois strongly opposed efforts to make the Philippines, which were annexed from Spain after the Spanish–American War, an American territory.

Dubois first supported independence for the Philippines, but after a 1905 visit, he declared that Filipinos could not rule themselves and advocated selling the islands to Japan.

Dubois broke with most Democrats of the day and supported President Theodore Roosevelt's agenda of environmental conservationism.

Caused in no small part by Dubois' obsession with anti-Mormonism, Democrats in Idaho suffered significant electoral losses during his second term in the Senate.

Dubois lived the rest of his life in Washington, D.C. and made attempts at writing and business, which largely failed.