Morawiecki told a news conference that the new grouping would bring together 40 lawmakers and one senator.
"Together, 40 deputies and one senator have decided to establish a parliamentary group," he said. "It will be the political forum for the activities of the Development Plus association."
The former prime minister said he and his allies wanted to focus on challenging Prime Minister Donald Tusk's government rather than becoming embroiled in internal disputes within the conservative opposition Law and Justice (PiS) party, which governed Poland from 2015 until losing power in the 2023 parliamentary election.
'Plotters and splitters'
"In recent times, we have witnessed very strange party games that are completely unnecessary," Morawiecki said, accusing unnamed "plotters and splitters" within PiS of trying to divert attention toward internal party affairs.
"We do not want to engage in these party squabbles," he said. "We want to direct the focus of our attack toward Donald Tusk's very bad government."
Morawiecki said the new parliamentary group would provide a political platform complementing the policy and think-tank work carried out by Development Plus.
The announcement follows moves by PiS leaders to discipline members linked to Morawiecki's association.
PiS spokesman Rafał Bochenek said on Tuesday that the party's leadership had approved a list of 44 members who failed to submit, by the required deadline, declarations confirming they did not belong to outside associations.
The cases were referred to the party's disciplinary spokesman for individual review, he said.
Bochenek told reporters that, despite earlier indications from party leaders, the politicians had not automatically lost their PiS membership and formally remained members while disciplinary procedures continued.
Morawiecki dismissed the proceedings as irrelevant.
"Some party procedures are under way. We're not interested in them. Let them do what they want—we're looking ahead," he said.
He argued that voters were more concerned with issues such as economic growth, jobs, housing and national security than with internal party disputes.
"Our task is to show what mistakes, irregularities and missed opportunities this government is responsible for," Morawiecki said. "We are very well prepared to do that."
Morawiecki said last Friday he had refused to sign what he described as a party "loyalty declaration" and had offered to step down as one of PiS's deputy leaders.
His Development Plus grouping would win 7.5 percent of the vote and enter parliament if elections were held now, according to a survey.
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Source: TVP Info, IAR, PAP