He called for the vote after his political ally, the liberal Warsaw mayor, lost Poland's presidential election to conservative Karol Nawrocki.
"We are starting the session in a new political reality," Tusk said, at the start of a cabinet meeting in Warsaw.
"The political reality is new, because we have a new president. But the constitution, our obligations and the expectations of citizens have not changed. In Poland, the government rules, which is a great obligation and honour."
Tusk's government runs most of the day-to-day matters in Poland. It also exists separately from the presidency, but the president holds power to veto laws and influence foreign policy, and Nawrocki's win will make it extremely difficult for Tusk to press his pro-EU agenda.
There are already questions about whether Tusk's fragile coalition can survive until the next scheduled parliamentary election at the end of 2027.
The decision to call a confidence vote is apparently an attempt by Tusk to try to reassert authority in a shifting political situation where some of his coalition partners might be less likely to want to stick with him.
Tusk oversees a coalition of several parties spanning an ideological divide, from left-wing progressives to centrists to agrarian conservatives. The divided coalition has failed to agree on some issues and the government has failed to fulfil some of Tusk's key promises, including a liberalisation of the restrictive abortion law.
Nawrocki, who was supported by US President Donald Trump, won 50.89 per cent of votes in a tight race against Warsaw Mayor Rafał Trzaskowski, who received 49.11 per cent.
The election revealed deep divisions in the nation along the eastern flank of NATO and the European Union.
Nawrocki, who is set to take office on August 6, is expected to shape Poland's domestic and foreign policy in ways that could strain ties with Brussels while aligning the central European nation of nearly 38 million people more closely with the Trump administration.
Trump welcomed his election, saying on his social media platform Truth Social: "Congratulations Poland, you picked a WINNER!"
Nawrocki replied to Trump on X, saying: "Thank you, Mr President. Strong alliance with the USA, as well as partnership based on close co-operation are my top priorities."
AP
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