President Lech Kaczynski said he would formally accept his twin brother's resignation in two or three hours after his address to parliament. Outgoing Cabinet ministers will perform their duties until a new government is formed.
Poland's new parliament will start work later on Monday.
The identical twin brothers' Law and Justice party was defeated by Donald Tusk's center-right Civic Platform in the early October 21 election. Tusk is expected to be Poland's next premier, promising pro-business reforms and closer ties with the European Union.
Tusk is in talks with Peasants' Party led by Waldemar Pawlak on the formation of a majority coalition. Pawlak could receive the posts of deputy prime minister and economics minister in a new government, which Tusk will have to form within two weeks after being designated premier.
The two parties have 240 seats in parliament together, with 231 votes being required to approve a government.
