Ben Ali and his wife Leila Trabelsi, charged with plundering state coffers after the discovery of money and jewellery at their palace outside Tunis, were also fined a total of 91 million dinars (45.5 million euros/$66 million dollars).
Calling the conviction a "parody of justice" and "political liquidation," Ben Ali said it "expresses the blind hatred of the past that fails to hide the lack of any vision of the future."
US State Department spokeswoman Victoria Nuland argued however: "Just the fact that there was a legal process is already progress" over Tunisia under Ben Ali, toppled by a popular uprising in January that sparked a wave of revolts and reform movements across the Arab world.
"If you look at where we were with justice and accountability issues with Tunisia as recently as six months ago, the fact that there was a trial, the fact that... it was an accountable legal process is a big step forward," she said.
But Mouhieddine Cherbib of a France-based Tunisian rights group described the trial as "a big disappointment, the kind of charade of summary justice that the dictatorship had accustomed us to."
Tunisians "wanted a real trial, a fair one... a trial of the dictatorship with people who were tortured appearing as witnesses -- a justice system from which you learn something," Cherbib said, adding that high treason would have been a more appropriate charge.
The daily La Presse described the pair's sentencing as "a downpayment of 35 years each."
The alleged ill-gotten gains amassed by the ousted president and his wife during Ben Ali's 23-year rule have been estimated as being worth about a quarter of Tunisia's gross national product.
Monday's trial was the first of many cases expected to be brought against Ben Ali as well as top members of his regime on allegations including murder, torture, money laundering and trafficking of archaeological artefacts.
Of the 93 charges Ben Ali and his inner circle face, 35 will be referred to a military court, a justice ministry spokesman said.
A case targetting Ben Ali only, involving weapons and drugs allegedly found in a presidential residence in Carthage, was postponed to June 30 to allow his lawyers more time to prepare.
Judge Touhami Hafi said the sentences, nearly twice the 20 years that had been widely predicted, would take immediate effect even though the couple are in Saudi Arabia, which has so far ignored Tunisia's extradition requests.
Another Ben Ali lawyer, in Beirut, denounced the verdict as farcical.
"This is a joke," attorney Akram Azoury told AFP. "You don't retaliate to a joke. You just laugh."
The 74-year-old former president denies any wrongdoing and in a statement released Monday said he had not intended to go into exile but was "duped into leaving Tunis."
Monday's conviction was seen as an attempt by the transitional government set up after Ben Ali's departure to appear pro-active to discontented Tunisians.
"This trial is a pretext, a charade to show that they are taking action," Beatrice Hibou, a senior researcher at the CERI international relations think-tank, told AFP.
"It reflects the current tension in Tunisia. Tunisia is seeing a power struggle between the social movement and the old system that wants to continue" -- with many of the former regime still in the administration and justice system.
Ben Ali's dramatic departure came less than a month after the self-immolation of Mohamed Bouazizi, a 26-year-old street vendor whose protest over unemployment unleashed already-simmering popular anger against Ben Ali.