Elections to the 55th Parliament of New South Wales were held on Saturday, 26 March 2011. The 16-year-incumbent Australian Labor Party government led by PremierKristina Keneally was defeated in a landslide by the Liberal–NationalCoalition opposition led by Barry O'Farrell. Labor suffered a two-party swing of 16.4 points, the largest against a sitting government at any level in Australia since World War II. From 48 seats at dissolution, Labor was knocked down to 20 seats—the worst defeat of a sitting government in New South Wales history, and one of the worst of a state government in Australia since federation. The Coalition picked up 34 seats to win a strong majority, with 69 seats. It is only the third time since 1941 that a NSW Labor government has been defeated.
On 18 October 2008, four state electorates (Lakemba, Ryde, Cabramatta, Port Macquarie) went to by-elections as a result the resignation of the Premier, two of his ministers, and an independent who left after winning a federal by-election. The results in Ryde, Cabramatta, and Lakemba showed the largest by-election swing against Labor in its history. The results showed a significant swing towards the Liberal Party with a swing of 22.7 percentage points in former health minister Reba Meagher's seat of Cabramatta, but was retained by ALP candidate Nick Lalich, and a swing of 13 points against Labor in former premier Morris Iemma's seat of Lakemba, also retained by an ALP candidate, Robert Furolo. Ryde, once a safe Labor seat, with a swing of 23.1 points delivered former deputy premier John Watkins' seat to Victor Dominello. Peter Besseling, the independent candidate, won Port Macquarie, left vacant after the resignation of Nationals-turned-independent member Robert Oakeshott, over the Nationals by a two-party margin of 54.5–45.5%, despite a swing of 23.7 points to the Nationals. On 19 June 2010 a by-election in the electoral district of Penrith was triggered as a result of the resignation of Labor Party MP Karyn Paluzzano, with Liberal candidate Stuart Ayres winning the seat with a two-party-preferred swing of more than 25 points, the biggest swing against an incumbent government in New South Wales history, until the 2013 Miranda by-election which eclipsed it with a 26-point two-party swing against the Liberal/National government.
The Liberal and Nationals Coalition launched their campaign on 20 February 2011 at the Joan Sutherland Performing Arts Centre in Penrith within the electoral district of Penrith with the slogan: "Real Change for NSW". In attendance for the launch were both Liberal and Nationals Leaders O'Farrell and Stoner as well as federal Liberal Party leader Tony Abbott, former Liberal Premiers and Leaders Greiner, Fahey, and Chikarovski.
The Coalition had been leading in opinion polling for almost three years, and were unbackable favourites throughout the campaign to win the election. The final Newspoll had support for Labor at an all-time low with 23 percent of the primary vote and 35.9 percent of the two-party vote. Bookmakers were paying $1.01 for a Coalition win with Labor getting as much as $36 and one agency even paid out the winnings and declared the winner a week earlier. At one point, Labor was widely predicted to win as few as 13 seats, seven less than the actual result. According to several pollsters, Labor was in danger of losing several seats where it had not been seriously threatened in decades, as well as several that it had held for a century or more.
The Liberal/National Coalition won the largest proportional number of seats in NSW state history with 69 of 93 seats in the lower house—in contrast, Labor won 69 of 99 seats at Neville Wran's second "Wranslide" in 1981 election. Labor won 20 seats, the lowest for Labor in NSW Parliament in over a century, and the worst defeat that a sitting government in NSW has ever suffered. Many prominent Labor MPs and ministers lost their seats including Verity Firth, David Borger, Matt Brown, Jodi McKay, Virginia Judge, Phil Costa and Kevin Greene. In the process, the Coalition took dozens of seats in areas considered Labor heartland, such as western Sydney and the Upper Hunter—some on swings of well over 10 per cent. The Liberals actually won 51 seats, enough for a majority in their own right—the first time the main non-Labor party in the state had achieved this since adopting the Liberal banner in 1945. Although O'Farrell thus had no need for the support of the Nationals, he opted to retain the Coalition.
In the upper house however, where half of the chamber was up for election, the landslide was not enough to deliver a Coalition majority. Three additional votes outside of the Liberal/National Coalition were required to pass legislation. The balance of power shifted from the Greens to the Shooters and Fishers Party and Christian Democratic Party. With two seats each held by the latter two parties, both needed to give legislative support if Labor and the Greens opposed legislation.
Where a Member of the Legislative Assembly or Legislative Council did not renominate to contest the election, their term ended at the dissolution of the parliament. Members who confirmed their retirement were:
Newspoll polling is conducted via random telephone number selection in city and country areas. Sampling sizes consist of around 1200–1300 electors. The declared margin of error is ±3 percentage points.