The election resulted in a sweeping victory for two opposition parties: the right-wing, national-conservative Law and Justice (PiS) and the centre-right, liberal-conservative Civic Platform (PO).

The 2005 Sejm was elected by proportional representation from multi-member constituencies, with seats divided among parties which gain more than five percent of the votes using the d'Hondt method.

Discontent with high unemployment, government spending cuts (especially on health, education and welfare), affairs related to privatizations was compounded by a series of corruption scandals, the most serious of them being Rywin-gate.

All opinion polls suggested that the governing SLD-UP coalition would be heavily defeated at these elections and that the right-wing parties would win a large majority.

The BBC commented on election day: "The two centre-right parties are both rooted in the anti-communist Solidarity movement but differ on issues such as the budget and taxation.

Law and Justice, whose agenda includes tax breaks and state aid for the poor, has pledged to uphold traditional family and Christian values.

Had the two leading parties been able to form a coalition as expected, it would have had 63 percent of seats in the Assembly, just short of the two-thirds supermajority required to carry out constitutional reform.

Although PiS and PO were the clear winners, their vote was very unevenly distributed, being overwhelmingly concentrated in the cities, particularly Warsaw and the southern industrial areas around Kraków and Katowice, but also including Gdańsk, Gdynia, Poznań, Wrocław and Szczecin.

Negotiations between PiS and PO about forming a government collapsed in late October, precipitated by disagreement regarding who would be speaker of the Sejm.

The PO also opposed a "tactical alliance" between the PiS and the Self-Defense (Samoobrona) party, which shared eurosceptic and populist sentiments, although differing on economic policy.

The SLD's severe defeat sent the party into a sharp decline from which it has never fully recovered; it lost all of its remaining seats in 2015 though it regained some ground in 2019 as part of Lewica, and the Polish left-wing would not govern until New Left, formed from the merger of the SLD and Spring, entered Tusk's third cabinet as a junior coalition partner following the 2023 parliamentary election.