In the 1940 Alberta election, the Social Credit Party split the popular vote with the Unity Party, a Liberal-Conservative coalition, but won a majority of seats. The CCF did not fare as well. The party's association with the fallen UFA diminished its popularity, and its policies did not differ significantly from Social Credit's. In other provinces, the CCF did not face these obstacles, and in Saskatchewan, the CCF formed the government. Federally, the CCF tried to cooperate with Social Credit, but bitterness between Premier William Aberhart and William Irvine prevented such an alliance in Alberta.
Despite these obstacles, the CCF gathered momentum in Alberta. In the 1944 provincial election, the party ran candidates in each riding. They received twenty-five percent of the popular vote but won only two seats. The political climate favoured Social Credit, whose policies had shifted against socialism under Manning. The Unity Party was disintegrating and had turned toward the government to block the rise of the CCF. As a result, the CCF remained the only viable opposition to the Social Credit government.
In the post-war era, the CCF was divided over whether to tone down its socialist rhetoric and distance itself from more militant communists. The general public were behind Social Credit's commitment to reducing taxes and expanding Alberta's economy. The Alberta CCF argued for higher taxes on oil and gas production, but it stopped short of advocating the nationalization of the industry. More radical CCF members became disillusioned over their party's more moderate stance and did not renew their memberships. With less money and fewer organizers, the Alberta CCF could not mount an effective opposition in subsequent elections.
The CCF became the New Democratic Party (NDP) in 1961. The federal party's new leader, T.C. Douglas, represented unionist causes, and its new program called for more economic reforms than the party's Winnipeg Declaration of 1956. The Waffle Manifesto, which the party drafted in 1969, emphasized the need to protect Canada from foreign exploitation. The NDP advanced this cause particularly in Alberta, where the Social Credit government had allowed American companies to dominate the oil and gas industry. Yet the majority of Albertans, many of whom worked for these companies, supported the Manning government's lack of intervention.
From 1968 to 1984, the Alberta New Democrats continued under their dedicated leader Grant Notley. He was the party's only elected representative from 1971 to 1982.
Ray Martin assumed the party leadership after Notley died in a plane crash in 1984. The Alberta NDP took sixteen seats in the 1986 provincial election to become the Official Opposition. The party maintained the same number of seats in 1989 but was wiped out in 1993. Since then the NDP has held onto its longstanding base of support in Edmonton, returning two MLA's, including party leader Raj Pannu, to the Legislature in 2001.