Sylvia Bongo, 62, and 33-year-old Noureddin Bongo were taken into custody shortly after the 2023 coup that ousted Ali Bongo, who had ruled Gabon since 2009.
Previously, Bongo served as president of the Central African nation for more than four decades before dying in office.
Sylvia and Noureddin were accused of crimes including embezzlement of public funds and money laundering, which they reject.
They were detained for nearly two years before being transferred to house arrest in May and then flown with Ali Bongo to Angola, which said it had taken the family in “for humanitarian reasons.”
The family are currently in Britain, according to Reuters.
Ten more people are being put on trial in Gabon’s capital Libreville this week on similar charges.
Lawyers for the Bongos have denounced the proceedings against them as an illegal “show trial.”
“This verdict was predetermined in the office of President (Brice) Oligui Nguema a long time ago – today was merely a rubber-stamping exercise,” Noureddin Bongo said in a statement on Wednesday.
Maixent Essa Assoumou, president of the Specialised Criminal Court that tried the Bongos, said the verdict was “absolutely not an act of revenge, but a restoration of order.”
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Sylvia and Noureddin Bongo both have French citizenship and have brought complaints in Paris accusing Gabonese authorities of arbitrary detention and torture.
The 2023 coup in Gabon was one of eight in West and Central Africa between 2020 and 2023.
Nguema, the coup leader, was sworn in for a seven-year term as president in May after winning an election with nearly 95% of the vote.
