Samak Sundaravej yesterday made a U-turn by rejecting any further nomination for the post of prime minister while planning to resign as People Power Party leader shortly, sources said.
Theerapon Nop-ampa, who served as his secretary-general when Samak was prime minister, confirmed the ex-premier would also quit as party leader.
Theerapon quoted Samak as saying that he had done his best as PPP leader in protecting democracy.
"From now on, everything and every decision will depend on the PPP," he said.
MPs from the ruling party are to meet this morning to discuss the PPP's next move in response to Samak's decision.
His decision came after government MPs yesterday failed to form a quorum in a meeting scheduled to select a new PM. All MPs from the PPP's five smaller coalition partners and many from the ruling party were absent.
House Speaker Chai Chidchob postponed the meeting until Wednesday.
Somsak Kietsuranont, a PPP executive member, said yesterday it was understood that Samak had decided not to accept his party's nomination to be premier again.
"It is understood that Khun Samak will no longer want to be reinstated as prime minister [as a result of] the parliamentary session on Friday morning," he said.
A well-informed PPP source said it was highly likely that Samak would resign from the party soon.
Samak was on Tuesday disqualified by the Constitution Court, which found him guilty of violating the charter by hosting TV cooking shows while in office.
PPP executives, minus Samak, met yesterday afternoon and agreed the party leader should not accept any further nomination for the premiership, according to another party source.
It was also agreed that Samak should pick one of the three senior PPP figures - deputy leaders Somchai Wongsawat and Sompong Amornwiwat and party secretary-general Surapong Suebwonglee - to become the party's nominee as next prime minister.
Yesterday's meeting assigned Somchai, Sompong and Surapong to inform Samak in person about the resolution and to report about their discussion with him at the next party meeting, according to the source. As of press time, the trio had not met Samak at his home.
However, more than 80 party MPs who are close to banned influential politician Newin Chidchob remained firm about their support for Samak as prime minister.
Newin's faction favours Surapong as the party's candidate for PM while the rest plan to nominate Somchai, said a party source. However, if faced with strong opposition for Somchai's connection to ousted premier Thaksin Shinawatra, the group would instead nominate Sompong.
Samak arrived at Parliament in the morning to attend the House meeting. He managed to sneak into the building, avoiding several reporters and his supporters gathering at the car park waiting for his arrival.
He left the compound shortly after 10am. The ousted premier appeared tense and refused to answer questions from reporters.
Instead, Samak stared at reporters with a stern face, prompting party MP Nisit Sinthiprai, who came to send him off, to say: "Smile a bit, Mr Leader."