Samak's chances of becoming prime minister improved significantly after Banharn Silpa-archa, the head of the Chart Thai Party, withdrew from the race saying his party was unanimously behind Samak.
Samak, who has a controversial past and his own weekly TV cooking show, came out of retirement late last year to head the PPP and lead it to victory.
He is currently facing allegations of corruption during his tenure as Bangkok mayor.
As the deputy prime minister in 1992, he condoned the firing of live rounds into a crowd of student demonstrators in Bangkok. Scores were killed in that incident.
The Thaksin-backed PPP won the most number of seats in last month's parliamentary elections and formed a six-party coalition government to gain two-thirds control of the lower house.
|Analysts have cast doubt on how long |
Samak will stay in the post [AFP]
Some analysts believe the PPP is a thinly-veiled version of Thaksin's Thai Rak Thai, which was dissolved by court order in May last year, and that Samak's days as prime minister will be numbered.
"He's a frontman, he is an expedient choice, a trouble-shooter to get through this rough patch for Thaksin but he's not here to stay for the long-haul and I think he knows it," Thitinan Pongsudhirak of the Institute of Security and International Studies told the AP news agency.
Thaksin's wife, who went on trial in Bangkok last week on charges of corruption, has said her husband plans to return to Thailand from self-imposed exile in May.