De Lima, 63, has been in detention for the past six years and despite her acquittal, De Lima will not immediately be released because of another case pending in court.
De Lima was charged in 2017, just a few months after she launched a senate investigation into Duterte's "war on drugs", during which thousands of users and dealers were killed, many by police or in mysterious circumstances.
She was widely considered by human rights groups as a political prisoner.
"Thank you, thank you, more prayers," De Lima said as she emerged from the court room, in live streamed comments.
"I'm still asking for even more prayers for another case. Glorious day, glorious day, beginning of my vindication," she said.
An incensed Duterte had repeatedly accused her of being involved in the drug trade during televised speeches, which De Lima dismissed as a vendetta.
De Lima, a former justice minister who won several human rights awards, has said the charges were trumped up and designed to silence her.
In 2021, a court dismissed one of three drugs cases filed against De Lima that stemmed from Duterte's allegations, which led to multiple online hate campaigns against her.
Reading a statement De Lima, her lawyer, Filibon Tacardon, said "I have no doubt from very beginning I will be acquitted".
He said De Lima cried as she heard of the acquittal.
