The case, launched by Maurice Blackburn, claimed Roundup's active ingredient glyphosate caused the cancer of more than 800 Australian non-Hodgkin lymphoma patients.
But Justice Lee ruled there was not enough current evidence to say glyphosate is carcinogenic and capable of causing non-Hodgkin lymphoma in humans.
Bayer, which acquired Roundup's producer Monsanto in 2018, have repeatedly said their herbicide product had been rigorously tested and was safe when used as directed.
It was claimed more than 800 Australians suffered non-Hodgkin lymphoma because of Roundup.(Julian Smith/AAP PHOTOS)
The company's CropScience managing director Warren Inwood said Thursday's ruling was a win for Australian farmers who rely on critical farming tools like Roundup.
"These products underpin sustainable farming systems and support farmers in doing what they do best - putting food on the tables of Australians every day," he told reporters outside court.
Maurice Blackburn lawyer Lee Taylor said class action members were disappointed but the law firm would review the judge's decision.
Justice Lee only needed to consider the question of general causation - not the specific claims of lead applicant Kelvin McNickle or the other class action group members.
Mr McNickle, a 40-year-old Queensland man, said he was diagnosed with non-Hodgkin lymphoma in 2018 after allegedly using Roundup as a child and in his working life.
Justice Lee noted Mr McNickle's story but made clear his judgment was not directly about the Queensland man.
Instead, he had to consider more generally whether exposure to Roundup or herbicide products with glyphosate would increase a person's risk of developing non-Hodgkin lymphoma.
Justice Lee said he made his findings after only assessing the scientific evidence brought forward by the parties.
"(It) can only represent a snapshot of the state of scientific knowledge at the time," Justice Lee said.
The science was "not all one way" and some of the expert witnesses conceded there were possible links between glyphosate and cancer in humans, the judge said.
"One cannot foreclose the possibility that further research may reveal a compelling link,"Justice Lee said.
But the judge ultimately ruled on the state of the current evidence, and on the balance of probabilities, he could not determine there was a causal link between Roundup and cancer.
The judge ordered the class action proceedings be dismissed but reserved his decision on costs.
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