The Saskatchewan Progress Party (SPP) is a liberal political party in the Canadian province of Saskatchewan. It was founded in 1905 as the Liberal Party of Saskatchewan, and retained that name until members voted to change it in 2023. Until 2009, the party was affiliated with the Liberal Party of Canada.

The Liberals were a dominant force in Saskatchewan politics during the first half of the twentieth century, forming government for all but five years between 1905 and 1944. With the emergence of the Co-operative Commonwealth Federation (CCF) under Tommy Douglas' leadership, the Liberals spent the following two decades in Opposition before forming two more majority governments from 1964 to 1971. However, the party lost influence in the latter stages of the twentieth century. Although it reached Opposition status again in the mid-1990s, even that term was disrupted when much of the caucus abandoned the party to form the new Saskatchewan Party in 1997. The 1999 election marked the last time any Liberals were elected to the Legislature.

The Liberal Party dominated Saskatchewan politics from the province's earliest days. Saskatchewan entered Confederation in September 1905 alongside neighbouring Alberta. Both provinces were carved out of the Northwest Territories; territorial premier Frederick Haultain had advocated for the creation of one large western province called Buffalo, but Wilfrid Laurier's federal Liberal government opted to create two provinces instead, wary of the potential strength of a province the size of Buffalo. Haultain responded by seeking the premiership of Saskatchewan under the banner of his Provincial Rights Party, but Saskatchewan voters opted in 1905 for the provincial Liberal Party under the leadership of Walter Scott. This marked the beginning of a long Liberal dynasty in the new Prairie province—the party provided six of the province's first seven premiers.

With the Liberals a strong force at the federal level, Saskatchewan voters appear to have preferred a provincial government that had influence at the national level, and there was crossover with Liberal premiers like Charles Dunning and Jimmy Gardiner moving on to key federal cabinet positions. As a consequence, the provincial Liberals presided over the province at a time of tremendous growth as a rapidly expanding population driven by immigration—the province became the third most populous in the country after Ontario and Quebec—established a large agricultural economy.

One of the keys to Liberal success was their close relationship with immigrant communities and especially with the largest farmers' lobby in the province, the Saskatchewan Grain Growers' Association. While United Farmer governments took power in both Alberta and Manitoba during the 1920s, and while the agrarian Progressive Party performed well in Saskatchewan at the federal level, the direct entry of farmers into provincial politics was fended off for longer in Saskatchewan by Liberal leadership attuned to farmers' organizations. Early Liberal premiers were even known to invite key agrarian organizers to the cabinet table.

The Liberals also stood against a rising tide of nativist sentiment in the province in the 1920s. While the Ku Klux Klan gained a foothold in the province—the organization had 25,000 members in Saskatchewan by 1929—and fomented discriminatory attitudes towards French, Catholic, and Eastern European settlers, Premier Gardiner defended his government's immigration policies and called the Klan both a foreign entity and a tool of the provincial Conservative Party. The Conservatives were reported to have aided Klan organization by supplying it with membership lists, and the party itself developed a nativist platform in the late 1920s, promising to protect British, Anglo-Saxon values. The Liberals were also heavily criticized for years of blatant patronage, which helped to move farmers closer to greater political participation and, more immediately, solidified a strong anti-Liberal bloc in the province. In the 1929 election, although the Liberals managed to win the most seats with 28, they fell short of a majority for the first time. They proved unable to gain the confidence of the Legislature, resulting in a coalition government under Conservative premier James T.M. Anderson—his party won 24 seats, and gained the support of the handful of Progressive and Independent members to form a coalition that they termed the "Co-operative" government.

Anderson's government took power at the outset of the Great Depression, which proved to be especially severe for the Prairie provinces and which provided the Liberals with ample opportunity to criticize the government's inability to contend with the crisis. In 1932, Anderson even invited Gardiner's Liberals into his coalition, but Gardiner refused. At the same time, a new political party was gaining momentum in the province. In 1932, farmers with United Farmers of Canada voted to formally enter politics, and after a merger with the Independent Labour Party did so under the banner of Farmer-Labour; the new party became a founding member of the Co-operative Commonwealth Federation (CCF) that same year. The party was explicitly socialist, rapidly changing the dynamics of provincial politics.

Gardiner and the Liberals were able to return to power in 1934; the Conservatives failed to return a single member, and Farmer-Labour became the Official Opposition with five members to the Liberals' fifty. After the election, Farmer-Labour officially adopted the CCF party name. Almost immediately, Gardiner had to contend with the passage through Saskatchewan of the On-to-Ottawa Trek, a 1935 convoy meant to take the concerns of unemployed workers directly to the federal government. Prime Minister R.B. Bennett declared that the trekkers would not proceed past Regina, which acted as the headquarters to the Royal Canadian Mounted Police. Gardiner protested, predicting a riot. He was proven correct on July 1 1935, when the Regina Riot led to two deaths and hundreds of injuries.