Thai Prime Minister Samak Sundaravej's five-month-old government was in disarray Thursday after the foreign minister resigned following a series of bruising court defeats for the Cabinet.

Foreign Minister Noppadon Pattama became the third top official in the ruling People Power Party (PPP) forced out of office in less than 48 hours due to the government's legal troubles.

The party's deputy leader Yongyut Tiyapairat, who was a former speaker of parliament, was banned from politics for five years Tuesday, after the Supreme Court upheld vote buying charges against him.

The following day, health minister Chiya Sasomsub was removed from office by another top court, which found that he had illegally concealed his wife's assets.

But Noppadon's court loss carries potentially damning implications for the entire Cabinet.

The Constitutional Court ruled Tuesday that Noppadon and the entire Cabinet had violated the charter by failing to seek parliamentary approval for a deal with Cambodia over a disputed temple on the border.

Noppadon had signed the agreement last month, which was approved by the Cabinet and military chiefs, supporting Cambodia's bid to seek World Heritage status for the 900-year-old Preah Vihear temple.

The verdict sparked public calls for the entire Cabinet to resign, and the opposition Democrat Party said it was considering an impeachment motion to force them from office.

In announcing his resignation, Noppadon said he hoped his leaving office would spare the rest of the government.

"I want to see national reconciliation. In order for the government to continue working to solve the country's problems, I resign," he said in remarks broadcast on national television.

"I insist that I have done nothing wrong. I have not sold the country out. I love Thailand, and would not cause any damage to the country," he added, visibly emotional.

Samak declined to answer reporters' questions, but analysts said the string of legal defeats could force him into a major Cabinet reshuffle.

"This is the minimum of what the Samak government has to do," political analyst Thitinan Pongsudhirak of Chulalongkorn University said of Noppadon's resignation.

"Now the question is, is it enough? I think the resignation is intended to alleviate pressure for the resignations of the entire Cabinet."

"We will likely see a major reshuffle," he said. "If it is a major overhaul of the Cabinet configuration, it can buy Samak some time."

Samak's government is closely aligned with former prime minister Thaksin Shinawatra, who was toppled by the military in 2006 following months of protests.

Noppadon was Thaksin's personal lawyer until he was tapped to lead the foreign ministry.

Samak's victory in elections last December had raised hope for an end to more than two years of political turmoil that have battered the Thai economy.

Instead, it reopened the gaping social divide that had marked the Thaksin era, pitting his mainly poor and rural supporters against the Bangkok elite.

Nearly seven weeks ago, the same royalist protesters that had rallied against Thaksin returned to the streets, clamouring for Samak's resignation.

The so-called People's Alliance for Democracy is now calling for major changes to Thai democracy, saying 70 per cent of parliamentarians should be appointed to their post.

The demand highlights the stark political reality that if Samak were to dissolve parliament and call new elections, Thaksin's supporters would likely win again, analysts say.

The political turmoil has weakened investment in Thailand at a time of soaring inflation and weak economic growth.

The instability has battered the Thai stock market, with share prices on the main Stock Exchange of Thailand index down more than 17 per cent since the protests broke out.