Mr Thaksin was ousted in a military coup in 2006
The corruption trial of former Thai Prime Minister Thaksin Shinawatra has begun in Bangkok, almost two years after he was overthrown in a coup.
Mr Thaksin and his wife face charges related to a Bangkok real estate deal.
The couple deny any wrongdoing, saying the charges of abuse of power against them are politically motivated.
Meanwhile, a top member of the main party in the ruling coalition was found guilty of electoral fraud. The ruling could lead to the party's dissolution.
The Supreme Court banned former House Speaker Yongyut Tiyapairat, of the People Power Party (PPP), from politics for five years after finding he was guilty of vote-buying in 2007.
Thaksin Shinawatra on his return to Thailand
The ruling will put more pressure on the PPP-led six-party governing coalition, already weakened by accusations that it is too close to Mr Thaksin.
Under Thai election law, the ruling against Mr Yongyut opens the way for the Election Commission to investigate whether the whole party was guilty of electoral fraud. It could then be disbanded.
Mr Thaksin, a telecoms billionaire who owns the English football club Manchester City, returned to Thailand in February after 18 months abroad.
The military ousted him in September 2006, accusing him of corruption and abuse of power.
Mr Thaksin has since been living mostly in the UK, but his political allies won democratic elections late last year, facilitating his return to Thailand.
He, his family and his aides face a number of different allegations. Millions of dollars of his assets have remained frozen since charges were laid.
The case now before the Supreme Court relates to the purchase of a plot of land in the Thai capital.
The former prime minister is accused of using his political influence to help his wife buy the land from a state agency at a favourable price.
The couple, who could face lengthy prison terms if convicted, did not attend court, but their lawyer sounded a positive note.
"We are confident that our evidence will be enough to prove in the court that Thaksin and his wife are not guilty," Anek Khamchum told the AFP news agency.
But the courts have shown surprising tenacity in pursuing this first case, says the BBC's Jonathan Head in Bangkok.
The government has tried to weaken the case by arguing that the military-backed bodies which investigated Mr Thaksin had no legitimacy.
The courts have ignored that, and have even intervened to reverse other government decisions.
Many observers in Thailand are calling this a judicial revolution - where the courts are quietly being asked by the traditional elite to act as checks on the power of elected governments.
Mr Thaksin's own prospects dimmed significantly when three of his lawyers were jailed last month by the Supreme Court for offering a cash bribe in a cake box, our correspondent adds.
At the very least, Mr Thaksin's chances of making a political comeback are looking slim, our correspondent says.