Former deputy prime minister Somkid Jatusripitak, chairman of the Sang Anakhot Thai Party (SATP), will move to the Palang Pracharath Party to strengthen the PPRP's economic team, sources said.
SATP leader Uttama Savanayana and secretary-general Sontirat Sontijirawong are also expected to rejoin the ruling party.
Santi Promphat, PPRP secretary-general, on Friday said people who are capable and experienced are always welcome to help the party steer the country forward.
"Several experts, academics and economists have contacted us about joining the party," he said.
"They have realised the party intends to solve problems and improve the economy and people's well-being.
"Most importantly, we will move past conflicts. I believe Mr Somkid and Mr Uttama have the intention to serve the people's best interest, and they have asked to join the party. This will help strengthen us," the PPRP secretary-general said.
"There was no conflict between us in the past. There might have been a difference of opinion, [but] there is nothing wrong if we are reunited," Mr Santi said, adding the PPRP's executive committee will decide which position Mr Somkid will assume.
PPRP leader Prawit Wongsuwon on Friday met Mr Uttama and Mr Sontirat for talks about their return to the PPRP.
Gen Prawit wanted them to rejoin the party as quickly as possible, and their return is expected to be announced next week at a press conference, the sources said.
Gen Prawit wants the event to show that they are willing to put their past conflict behind them, in line with the party's policy, the sources said, adding Mr Uttama would be placed in charge of economic strategies while Mr Sontirat would handle political strategies.
The SATP was established early last year after Mr Uttama, ex-leader of the PPRP and his faction, including Mr Sontirat, a former PPRP secretary-general, were purged from the ruling party in 2020 to make way for Gen Prawit to take the lead.
Mr Uttama, who served as finance minister and Mr Sontirat, who was energy minister, also resigned from the cabinet.
Mr Somkid, who was deputy prime minister in charge of the country's economic affairs at the time, also stepped down from the government, citing health problems.
Previously, the SATP discussed forming alliances with several parties after it failed to reach a deal with the Thai Sang Thai Party led by Khunying Sudarat Keyuraphan.
The SATP was said to be negotiating with Thai Sang Thai over a possible merger.
But both parties failed to reach an agreement on key positions.
Meanwhile, the PPRP officially named Gen Prawit as its sole prime ministerial candidate for the coming general election during the party's general assembly on Friday.
The SATP recently also announced it would name party chairman Mr Somkid as one of its prime ministerial candidates for the polls.
Industry Minister and deputy PPRP leader Suriya Jungrungreangkit, a key figure of the Sam Mitr (Three Allies) faction, on Friday denied reports the group would defect to other parties.
"I confirm that the group will stay put at the party," he said.
In other news, Thanakorn Wangboonkongchana, the Prime Minister's Office Minister, on Friday said he has applied to join the United Thai Nation Party after resigning from the PPRP.
He said he wants to support Prime Minister Prayut Chan-o-cha bid to return to the same role after the next general election.