A jury in California has awarded more than $2 billion to a couple who claimed Bayer's glyphosate-based Roundup weed killer caused their cancer.
It is the third consecutive verdict against the company over the product and the largest to date.
The couple's legal team described the damages award as "historic," saying it totalled $2.055bn after adding in slightly more than $55 million in compensatory damages.
"The jury saw for themselves internal company documents demonstrating that, from day one, Monsanto has never had any interest in finding out whether Roundup is safe," said plaintiff's counsel Brent Wisner.
"Instead of investing in sound science, they invested millions in attacking science that threatened their business agenda."
Bayer acquired Roundup as part of its $63bn dollar purchase of Monsanto last year.
The company insists the glyphosate-based product is not linked to cancer and says it was disappointed with the verdict and will appeal.
Bayer-owned glyphosate developer Monsanto was convicted in the US in 2018 and 2019 of not taking necessary steps to warn of the potential risks of Roundup - their weed killer containing the chemical, which two California juries found caused cancer in two users.
"Unlike the first two Monsanto trials, where the judges severely limited the amount of plaintiffs' evidence, we were finally allowed to show a jury the mountain of evidence showing Monsanto's manipulation of science, the media and regulatory agencies to forward their own agenda despite Roundup's severe harm to the animal kingdom and humankind," said attorney Michael Miller, who was co-lead trial counsel along with Mr Wisner.
The German chemicals giant faces more than 13,400 US lawsuits over the herbicide's alleged cancer risk.