Security was increased in Thailand ahead of the court's verdict
Thailand's Supreme Court has ruled that former PM Thaksin Shinawatra's family should be stripped of more than half a contested $2.3bn fortune.
The court said $1.4bn (£910m) of the assets were gained illegally through conflict of interest when Mr Thaksin was prime minister.
The funds were frozen after Mr Thaksin's elected government was overthrown in a military coup in 2006.
Mr Thaksin, who is living abroad, has denied any wrongdoing.
The Supreme Court said "to seize all the money would be unfair since some of it was made before Thaksin became prime minister".
By Vaudine England, BBC News, Bangkok
By choosing to confiscate some, but not all of Mr Thaksin's known assets, the court has managed to dampen arguments from his "red shirt" supporters that the entire judiciary is suborned to a military-bureaucratic elite which intends to finish off Mr Thaksin once and for all.
But it will also weaken the government's demonisation of Mr Thaksin. It appears to be saying that the former prime minister did cheat on the hiding and increase of his fortune, but he was significantly and legitimately wealthy when he entered office. He remains a rich man by any standards.
What this verdict will not do is heal the divisions in this country, polarised by Mr Thaksin's hugely popular appeal and the threat this poses to the military-bureaucratic elite. The 2006 coup that deposed him continues to damage the legitimacy of the current military-backed government of Abhisit Vejajjiva - this basic issue also goes well beyond one man and his money.
The court took several hours to deliver its verdict, with security forces on high alert amid government predictions of violence by Mr Thaksin's red-shirted supporters if the court decision went against him.
The judges said that Mr Thaksin shaped government mobile phone and satellite communications policy to benefit his firms.
He abused his power to benefit telecoms company Shin Corp, which he owned then, earning wealth from shares sales in the company through "inappropriate means", they ruled.
The sale of Shin Corp to Singapore state investment firm Temasek in January 2006 was one of the main catalysts for widespread protests calling for Mr Thaksin to resign, and the government applied for the seizure of the proceeds from the sale.
The court dismissed defence arguments that the anti-corruption commission that instigated the proceedings against Mr Thaksin was illegitimate.
Mr Thaksin addressed his supporters from Dubai after the verdict.
"This is total political involvement. The government knew the result in advance," he said, according to Associated Press.
"I've been prepared for the result since yesterday. I knew that I would get hit, but they are kind enough to give me back 30 billion [baht]."
He had previously told them he would continue his political fight against the "military-bureaucratic elite" that deposed him - with or without his family fortune.
He has said the money he and his family earned was acquired legally. The full extent of fortune is unknown, but he is thought to be very wealthy.
Tensions in Thailand remain high. Tens of thousands of extra police have been placed in and around the capital, and in areas of the north-east of the country where some of Mr Thaksin's supporters are based.
2001: Elected prime minister
19 Sept 2006: Ousted in military coup
25 Sept 2006: Corruption investigation begins
11 June 2007: Thaksin family assets frozen
25 Aug 2008: Prosecutors ask Supreme Court to seize frozen assets
21 Oct 2008: Sentenced in absentia to two years for conflict of interest in land deal
26 Feb 2010: Court seizes $1.4bn of $2.3bn in contested assets
There were only small numbers of Thaksin supporters outside the court. The pro-Thaksin United Front for Democracy against Dictatorship (UDD), which leads the red shirts, has said it has no plans for any demonstration until mid-March.
Local media had predicted huge disruption, counting down to what they called "judgement day".
The judges looked at whether Mr Thaksin illegally deposited his fortune with family members because he was not allowed to hold company shares while prime minister, and whether his administration implemented policies to benefit his family's businesses.
They have also considered whether telecoms liberalisation measures unfairly benefited the country's main mobile phone service provider, then controlled by Mr Thaksin's family.
And they have investigated whether he unfairly promoted a $127m low-interest loan to neighbouring Burma to benefit a satellite communications company also controlled by his family.