Poland’s newly elected Parliament torpedoed a long-shot effort by right-wing forces on Monday to stay in power despite losing a general election, opening the way for the opposition leader, Donald Tusk, to take over as leader of the biggest and most populous country on Europe’s formerly communist eastern flank.
Legislators, as expected, rejected a new government proposed by the caretaker prime minister, Mateusz Morawiecki, whose party, Law and Justice, lost its parliamentary majority in an October election.
Mr. Morawiecki, who led Poland’s previous right-wing government, resigned after the election but was asked by Poland’s president, Andrzej Duda, an ally of Law and Justice, to stay on in a caretaker capacity and to try to form a new government.
Opponents of Law and Justice denounced Mr. Duda’s move as a last-gasp attempt by the defeated party to prolong its rule and appoint allies to positions in state institutions and companies.
In a final, desperate effort to keep the opposition from taking over, a commission formed by t he outgoing government to investigate Russian influence late last month recommended that Mr. Tusk and other leading opposition figures not be allowed to hold positions responsible for state security.
The vote in Parliament on Monday, however, ended the defeated party’s efforts to remain in power and left Mr. Tusk, a former prime minister and leader of the main opposition party, Civic Coalition, poised to take leadership of a new government.
After a day of often raucous debate, 266 legislators voted against the government proposed by Mr. Morawiecki and 190 for, far short of the majority it needed in the 460-member Sejm, the more important lower house of the Polish Parliament, to hang on. Opposition members chanted “Donald Tusk, Donald Tusk,” as the result was announced.
Mr. Morawiecki, ignoring demands from the speaker of Parliament that he stop talking and jeers from opposition legislators, delayed the vote with a lengthy defense of Law and Justice’s record and pleas that he be allowed to stay in office.
By rejecting Mr. Morawiecki’s proposed government, doomed to fail because of Law and Justice’s electoral defeat, parliament delivered a grave blow to Jaroslaw Kaczynski, the chairman of the defeated party, Poland’s de facto leader since 2015 and a bitter political enemy of Mr. Tusk.
In a speech to Parliament on Monday morning, Mr. Kaczynski pleaded with legislators to support Mr. Morawiecki, warning that Poland risked losing its independence to the European Union if Law and Justice did not continue governing the country.
Poland, he said, repeating his oft-stated view that the opposition serves foreign, particularly German, interests, would become a “dwelling area for Poles managed from outside from Brussels and in fact from Berlin.”
The Polish Constitution gives Parliament the right to nominate a prime minister if the president’s nominee fails to win support from legislators. Mr. Tusk is expected to be nominated by the Sejm on Monday evening and be confirmed by the body as prime minister when a confidence vote is held later in the week, probably on Wednesday.
The installation of a new government headed by Mr. Tusk could be a drastic shift away from Poland’s direction during eight years of Law and Justice rule, a period marked by close relations between the governing party and the Roman Catholic Church and by near-constant quarrels with the European Union over the rule of law and other issues.
Scope for change, however, will be crimped by the grip of Law and Justice appointees on the judiciary, powerful state bodies like the central bank, the national prosecutor’s office, the national broadcasting system and large state-controlled corporations like the energy giant PKN Orlen. Many of those appointments will be hard to reverse.
Mr. Tusk and his allies are divided on the issue of abortion, which was almost completely banned by the previous government, but share a common desire to restore the independence of the Polish judiciary, which was heavily politicized under Law and Justice, and repair relations with the European Union.
