A Portuguese judge on Monday charged former Prime Minister Jose Socrates with corruption and tax fraud and ordered that he remain in preventive custody.
Socrates' arrest on Friday shocked the country and his Socialist party, which hopes to win next year's election.
As a court official read out the judge's decision late on Monday, Socrates' lawyer, Joao Araujo, told reporters he considered it "unfair and unjustified" and said he would appeal.
Criminal Judge Carlos Alexandre, who presides over several separate high-profile investigations, delivered his decision after a three-day questioning marathon over suspected tax fraud, corruption and money-laundering.
The detention is the first involving a former premier in Portugal under democracy and follows other loud cases this year as prosecutors and judges intensify a fight against corruption in a country notorious for its slow justice system.
Police arrested Socrates, 57, who was premier between 2005 and 2011, at Lisbon airport late on Friday as he arrived from Paris where he has been living after his resignation.
Three other individuals linked to Socrates were also arrested, including his driver. Citing leaked police materials, local media said the driver is suspected of having transported large sums in cash by car from Portugal to Socrates in Paris.