The ruling party's spokeswoman Beata Mazurek has said that "it is not a secret that a proposal has appeared" for Deputy Prime Minister and Finance and Development Minister Mateusz Morawiecki to replace Szydło as prime minister, but she said the definitive decision on the matter "has yet to be made".
Polish Prime Minister Beata Szydlo has resigned, hours after surviving an opposition no-confidence motion.
On Thursday, party leaders were scheduled to hold a meeting over a government reshuffle. The meeting was expected to concern planned changes to the government, among other issues.
Mazurek said Szydlo, who had been prime minister since elections brought PiS to power in 2015, resigned shortly before Morawiecki's appointment.
Poland's ruling conservatives named in an expected move Finance Minister Mateusz Morawiecki as the country's new prime minister on Thursday as they gear up for a series of elections in the coming years.
Though Szydlo's government is riding high in opinion polls, ruling Law and Justice head Jaroslaw Kaczynski is thought to be advocating a change.
She is expected to formally tender her resignation to PiS-allied President Andrzej Duda on Friday, while the PiS-controlled parliament could approve Morawiecki's new administration by Tuesday, according to media reports.
Despite the criticism from overseas, Szydlo's eurosceptic government, in power for two years, was one of the most popular in Poland since the 1989 collapse of communism, largely due to low unemployment, increases in public spending and a focus on traditional Catholic values in public life.
The name of a new Polish prime minister will be disclosed on Thursday, the deputy Speaker of the lower house of Poland's parliament has said.
She noted that Szydlo will be offered an important position in the new government, without giving further details.
But it remains to be seen whether Poland, once a champion of democratic changes after the fall of Communism and now at loggerheads with the European Union over sweeping changes to state institutions, which critics say have subverted democracy and the rule of law, will change its relations with Brussels. Szydlo, however, is at the center of speculation that she and some of her ministers will be replaced in a government reshuffle in the near future.
The government shuffle comes ahead of parliamentary votes on Friday on two controversial laws that would give the government far-reaching powers over the judicial system.