The exiled leader is currently in living in Britain and has bought Manchester City, an English football club, during his time outside Thailand.
Thaksin and his wife face charges summarised as "misconduct of a government official and violation of a ban on state officials being party to transactions involving public interests".
He faces up to 10 years in jail and a fine of up to $1,800 should he be convicted.
The charges concern Pojaman's $22.3m purchase of land in central Bangkok from a unit of the Bank of Thailand in a 2003 auction at which other bidders dropped out.
Thaksin was the prime minister then.
|"The current situation is still not good for their safety and we have no desire to see disunity in the country"|
Pichit Chuenban, Thaksin's lawyer
The case arises from a ruling by Thailand's Asset Examination Committee that Thaksin and Potjaman broke laws preventing politicians in office from doing business deals with state agencies.
The couple deny the charges and Thaksin says he will not return to Thailand until the military hands control of the country to a civilian government after a general election.
Thaksin's lawyers argue the case should be postponed to next year, or 30 days after a new government takes office following the election, which is set to take place in December.
His return before an election could also cause trouble between his supporters and their opponents, they said.
"I have talked with my two clients and we agree that the best timing for them to return to fight the case is after the election," Pichit Chuenban, Thaksin's lawyer, said after the ruling.
"We reiterate that the current situation is still not good for their safety and we have no desire to see disunity in the country."
Sonthi Boonyaratglin, army chief and leader of the bloodless coup that led to Thaksin's exile, said his safety would be guaranteed on his return.
He said: "There should not be any problem for him to return. Everything has gone in accordance with the Asset Examination Committee and court process which people can understand."