With a crisis in the agriculture sector, Romanow appointed Lingenfelter as Minister of Agriculture and Food, and again as Government House Leader. As deputy premier, Lingenfelter was viewed as a likely candidate to succeed Romanow as leader of the Saskatchewan New Democratic Party, but in July 2000 he announced that he was leaving provincial politics and seeking opportunities in the private sector. He became vice-president of government relations for Calgary-based energy company Nexen on September 1, 2000. On October 30, 2008, Lingenfelter was the first candidate to announce his candidacy to replace Lorne Calvert as the Leader of the Saskatchewan New Democrats at the June 6, 2009 leadership convention. Lingenfelter was the first declared candidate with former party president Yens Pedersen entering second, MLA Deb Higgins entering third and doctor Ryan Meili entering fourth. Lingenfelter received the endorsement of over half of the party's caucus as well as a number of unions including the largest private sector union in Saskatchewan, the UFCW Local 1400 and the United Steelworkers. Lingenfelter was later nominated as the NDP candidate for the by-election in Regina Douglas Park. On September 21, Douglas Park voters elected Lingenfelter, giving him 50.25% of the total votes counted in a three-way race matching him against the Saskatchewan Party candidate, Kathleen Peterson, and the Green Party's Victor Becker Lau. Lingenfelter led the NDP into the 2011 provincial election. In the November 7 election, the Saskatchewan NDP was defeated, losing 11 seats. The NDP ended up winning nine of fifty-eight seats, its worst showing since 1982. It also tallied its lowest popular vote percentage since 1938. One of the losing NDP MLA's was Lingenfelter, who lost his seat to the Saskatchewan Party's Russ Marchuk by a 10-point margin. With the Saskatchewan Party landslide beyond doubt, Lingenfelter resigned as NDP leader on election night. He was the first CCF/NDP leader since World War II to have never served as premier.