However, 89-year-old Marcos can appeal the ruling and post bail, which would allow her to remain free while the case grinds through the country's notoriously slow justice system.
The verdict from the anti-graft Sandiganbayan court orders her to serve a minimum of six years behind bars over charges the Marcoses funnelled roughly $200 million through Swiss foundations decades ago.
Ferdinand Marcos, who along with cronies was accused of pilfering $10 billion from the Philippines, fled with his family to the US after a people's uprising ended his 20-year rule in 1986.
Marcos died in 1989 while still in exile. But his heirs later returned to Manila and have since staged a political comeback. Imelda Marcos is currently a congresswoman.
As a government official in the Marcos administration, Imelda was barred by law from having any financial interest from the Swiss foundations, said the ruling.
"The couple opened all those accounts in Switzerland, and they used pseudonyms to hide their ownership. The president chose William Saunders and Imelda Marcos used Jane Ryan," special prosecutor Ryan Quilala told reporters.
Her lawyers could not be reached, while a press aide told AFP there was no immediate comment.
Court officials said Marcos would be able to avoid incarceration by posting an as yet undetermined bail and has the right to appeal her conviction to the nation's highest legal authority, the Supreme Court.
The body has previously undone a case against Imelda, overturning a 24 year jail sentence in 1993 on graft charges. She ran for congress and won while her appeal was underway.
The family's notoriety stems back to Ferdinand Marcos declaring martial law in 1972. That allowed him to shutter the legislature, muzzle the free press and jail or kill those who dared to oppose his dictatorship.
In the decades since Marcos's ouster the effort to recover the pilfered money has been halting and uneven.
However, the Philippine Supreme Court in 2003 ordered $680 million in funds stashed by the Marcoses in Swiss banks handed to the government.
The funds had earlier been turned over by the Swiss judiciary after concluding that the funds were stolen from the Manila government.
The younger generation of Marcoses have led high-profile careers, despite the dark past associated with their name.
Imelda and Ferdinand's daughter Imee Marcos, is the governor of the family's northern stronghold of Ilocos Norte province and helped bankroll the 2016 election campaign of President Rodrigo Duterte, according to him.
Imelda's son, also named Ferdinand, almost won the separate election for vice president that year.
He has put the count under protest and hopes to run for president after Duterte's term ends in mid-2022.