The judge sentenced Najib to 15 years in jail on each of the four counts of abuse of power and five years in prison for each of the 21 charges of money laundering, all of which would be served concurrently.
Najib, 72, has been in prison since August 2022 after a conviction in an earlier case involving 1Malaysia Development Berhad, which he co-founded in 2009 while prime minister.
He has denied wrongdoing.
Najib was also fined 13.5 billion ringgit ($A4.2 billion) on Friday.
If he fails to pay, Najib faces another 10 years in prison.
Najib's lawyer said they plan to appeal the verdict.
Dressed in blue suit, Najib stood up and was calm when the sentencing was announced, slumping later back in his chair in the dock.
The ruling marked a major milestone in one of the world's largest financial scandals, which rippled across global markets and triggered investigations in the United States and other countries.
Najib denied any wrongdoing and maintained the funds were a political donation from Saudi Arabia and that he had been misled by rogue financiers led by Low Taek Jho.
Low, thought to be the scandal's mastermind, remains at large.
The judge said Najib's claim of a Saudi donation was "incapable of belief".
Four letters purportedly from the Saudi donor were forged and evidence clearly showed the funds originated from 1MDB, he said.
Justice Collin Lawrence Sequerah rejected defence arguments that Najib was an unwitting victim, duped by former 1MDB officials and Low.
Witness testimonies had pointed to an "unmistakable bond" between Najib and Low, who had played a pivotal role in the scandal and operated as "the proxy, the conduit, the intermediary and the facilitator" for Najib in 1MDB, the judge said.
The judge noted that Najib failed to take steps to verify the origin of the massive funds nor took action against Low.
Instead, Najib used the money despite its suspicious origins and took steps to protect his position, including by removing the then-attorney general and anti-corruption chief investigating the case, he said.
While Najib returned most of the funds to an offshore account where they came from, he said this was clearly staged to conceal the illicit origin of the funds.
with AP
