The Palang Pracharath executive decided to expel Thamanat Prompow and his faction to save the party, after he demanded substantial changes, deputy leader Paiboon Nititawan said on Thursday.
Mr Paiboon and party executive member Somsak Thepsutin both agreed the PPRP would be more united, more stable without Capt Thamanat and the 20 MPs under his control.
The party held an urgent meeting on Wednesday to expel the party secretary-general and his followers.
Mr Paiboon said the decision to part ways was made because the ousted secretary-general's demand for restructuring was unacceptable and it would have deepened conflict within the party.
He refused to give details on Capt Thamanat's demand. The Phayao MP has not since talked to reporters, but posted a Facebook message on Wednesday night thanking his supporters and the PPRP.
He did not say which party his faction would join. They have 30 days to find new homes if they wish to retain their seats in the House.
Mr Paiboon said the PPRP will inform the Election Commission of the expulsion.
The position of party secretary-general is now vacant. Mr Paiboon said party leader Prawit Wongsuwon would decide on the appointment of a new secretary-general.