Tusk, a former top EU official and the opposition's candidate for the new prime minister, made the declaration at a meeting of his liberal Civic Platform (PO) party on Monday.
He was speaking ahead of the first session of Poland's new parliament, which began at noon, public broadcaster Polish Radio's IAR news agency reported.
Tusk said: "We've waited eight years for this ... It's a special moment."
He added: "People will again be able to watch parliamentary debates, the actions of the democratically elected authorities, with calmness and trust."
Tusk, who leads the main opposition bloc, the Civic Coalition (KO), urged his party to "maintain determination" as it seeks to assume power as part of a broad coalition of pro-EU groupings.
He said: "I will expect you to show toughness, courage and determination in the fight to restore the appropriate status and importance to such institutions as local government, free courts and free media."
Tusk added: "There is a multitude of problems to be solved, but we are capable of meeting all the challenges."
He added that last month's elections offered "hope for hundreds of millions of people" deprived of "freedom, hope and democracy," state news agency PAP reported.
Poland to appoint new gov't
Poland’s ruling conservative Law and Justice (PiS) party won the parliamentary election on October 15, but lost its majority to an alliance of four pro-EU opposition parties led by Tusk's Civic Coalition.
President Andrzej Duda announced last week that the task of forming a new government would be given to current Prime Minister Mateusz Morawiecki.
As all other parties have ruled out entering into a coalition government with Morawiecki's Law and Justice, the current ruling party, in power since 2015, looks unlikely to be able to govern.
If Morawiecki is unable to win a vote of confidence in the lower house, the chamber will appoint another prime minister.
The job is expected to go to Tusk, who served as prime minister from 2007 to 2014.
(pm/gs)
Source: IAR, PAP
