"It's a historic judgment. It will benefit hundreds of thousands of victims put to jail under the emergency laws," he said.
But Kamrul Islam, her other lawyer, said the victory would be short-lived, with the government set to take the matter to the supreme court, a body that has in the past sided with the authorities.
"We will fight in the supreme court, although we have very dim hope for a positive verdict. In the past, the supreme court's appellate division has overturned all the high court verdicts in favour of the government," he said.
The former prime minister, who led the country from 1996 to 2001, is one of around 150 high-profile figures arrested as part of an anti-graft drive by the emergency government, which took office in January 2007.
Hasina, the leader of the Awami League party, went on trial for corruption late last month, facing accusations that she extorted $435,000 from a power company owner.
She has denied the charges, arguing that the military-backed emergency government was merely trying to destroy her political career.
Hasina faces a maximum 14 years in jail if convicted. The trial is expected to be concluded within the next two months, as stipulated by the country's emergency rules.
Khaleda Zia, the country's last elected prime minister, is also in detention on corruption charges. She and Hasina are bitter rivals, and have been blamed for 16 years of misrule and rampant corruption.
The country has been under emergency rule since January 11 last year, when polls were cancelled after months of violence over vote-rigging allegations made by the Awami League against Zia's Bangladesh Nationalist Party.