The nation's High Court found Najib, 72, guilty on four counts of abuse of power and 21 charges of money laundering related to more than $US700 million ($A1.0 billion) channelled into his personal bank accounts from the 1MDB fund.
Najib's defence team was expected to make mitigation arguments before sentencing later on Friday.
Najib, who served as prime minister from 2009 to 2018, is currently serving a prison sentence after being convicted in an earlier case linked to the 1MDB scandal, which led to his government's defeat in 2018.
He was sentenced to 12 years in prison in 2020 for abuse of power, criminal breach of trust and money laundering involving funds channelled into his accounts from SRC International, a former unit of 1MDB.
He began his sentence in August 2022 after losing a final appeal, becoming Malaysia's first former leader to be jailed.Â
The Pardons Board, a body that advises rulers on granting clemency, halved his sentence and sharply reduced his fine in 2024.
Najib set up the 1MDB development fund shortly after taking office in 2009. He had chaired 1MDB's advisory board and held veto power as finance minister while serving as prime minister.
The corruption case rippled across global markets and triggered investigations in the United States and other nations.
Authorities alleged the funds were used to finance Hollywood films and extravagant purchases including hotels, a luxury yacht, art and jewellery.
The scandal also hit Wall Street, with Goldman Sachs facing billions in fines for its role in raising money for 1MDB.
Najib denied any wrongdoing. He maintained the funds were a donation from Saudi Arabia and he had been misled by rogue financiers.
Earlier this week, Najib failed in his bid to serve his corruption sentence under house arrest. Malaysia's High Court ruled on Monday that a rare royal order for home arrest issued by the nation's former king was invalid because it was not made in accordance with constitutional requirements. Najib's lawyer has said they plan to appeal.
Originally due for release in August 2028 after his sentence reduction, Najib now faces a longer stretch behind bars.
