The New Democratic Party (NDP) and its predecessor the Co-operative Commonwealth Federation (CCF) have been the province's most successful provincial parties, winning twelve of the sixteen elections between 1944 and 2003. The national NDP was formed in 1961 and initially led by former Saskatchewan Premier, T.C. Douglas. The Saskatchewan CCF was reluctant to officially adopt the NDP name, which was finally adopted only after election losses in 1964 and 1967. The NDP, led by Woodrow Lloyd, remained in opposition to the Liberal government of Ross Thatcher from 1964 to 1971. While in opposition, the party criticized the government's privatization of various Crown corporations, the austerity measures after the 1967 election, and the introduction of deterrent fees on health care. The period was also a turbulent time for the party as the growing radicalism of the baby boom generation gave life to the Waffle Movement. The party tried to accommodate the group into its structure, but the Waffle's confrontational style made this ultimately impossible. The movement helped stimulate substantial debate over party policy: this, in part, contributed to programs later instituted by the Blakeney government, such as the Land Bank and the nationalization of part of the province's natural resource sector. Amid controversy, Woodrow Lloyd resigned as party leader in 1970; Allan Blakeney won the leadership contest over Roy Romanow, Waffler Don Mitchell, and George Taylor in one of most heated leadership contests in Saskatchewan history.
Benefiting from the unpopularity of the Thatcher government, the NDP swept to power in 1971, winning the highest percentage of vote in its history. Allan Blakeney became Premier, a position he held for the next eleven years. His government pursued a policy of interventionism in the province's resource sector. Royalty rates for natural resources were increased, and a number of Crown corporations were established in the sector - most notably SaskOil and the Saskatchewan Potash Corporation. The policy was highly controversial, especially the nationalization of a large percentage of the province's potash industry. The government also pursued development of the uranium industry, a move that upset large sections of the NDP's own membership. The government played a leading role in the constitutional negotiations that resulted in the patriation of the Canadian Constitution in 1982.
The Blakeley government was re-elected in 1975 and 1978, but defeated in 1982. The long-dormant provincial Progressive Conservatives, led by Grant Devine, swept the province and left the NDP with only nine MLAs, the party's worst result since its inception. The party was forced into opposition, but quickly rebounded in the polls, regaining its urban base and winning the popular vote in 1986; but it still had significantly fewer seats than the Conservatives owing to the overrepresentation of rural Saskatchewan in the Legislature. Roy Romanow replaced Blakeney as leader in 1987. The NDP challenged the increasingly unpopular government on its reliance on deficit budgets and over the sale of Crown corporations such as SaskEnergy. In 1991, the NDP returned to power as the Devine government was soundly defeated.
Inheriting a substantial debt, the NDP government attempted to improve the province's fiscal position by implementing a variety of unpopular cost-cutting measures and increased taxation; the most controversial measure was the conversion of many local hospitals into healthcare facilities. Succeeding in balancing the budget, the government was re-elected in 1995. It was again re-elected in 1999, but by the slightest of margins: the newly formed Saskatchewan Party had won the popular vote, although the NDP won more seats. The government was forced to enter into a coalition with the Liberal party to stay in power. The party lost nearly all of its rural seats as it was increasingly representing urban Saskatchewan. Romanow stepped down as party leader in 2001 and was succeeded by Lorne Calvert. With the Saskatchewan Party seemingly gaining momentum, the Calvert government was widely expected to lose; however, in November 2003 Calvert pulled off an upset, winning a fourth consecutive term in government and re-establishing a majority in the Legislature.