Now a federal judge has ruled that there was sufficient evidence for a jury to hear the case that the company's weed-killer, still sold across the United Kingdom, is causing cancer.
The decision by U.S. District Judge Vince Chhabria in San Francisco followed years of litigation and weeks of hearings about the contentious science around the safety of glyphosate.
The judge wanted to determine whether the science behind the claim that glyphosate can cause non-Hodgkin's lymphoma had been properly tested and met other requirements to be considered valid.
This case is a separate one from a class-action suit that involves more than 300 plaintiffs who argue that their exposure to Monsanto's weed killer caused them to also develop non-Hodgkin's lymphoma.
The outcome of Johnson's case will not affect the hundreds of other lawsuits in state and federal courts, but it may serve as an indicator of how the others might go.
"Moving forward, we will continue to defend these lawsuits with robust evidence that proves there is absolutely no connection between glyphosate and cancer", Monsanto Vice President Scott Partridge said in a statement.
Many government regulators have rejected a link between cancer and the active ingredient in Roundup - glyphosate. He peppered them with questions about potential strengths and weaknesses of research on the cancer risk of glyphosate. "The best study of human beings who, like Mr. Johnson, are licensed pesticide applicators, concludes that glyphosate has no association with non-Hodgkin lymphoma".
In his ruling Tuesday, the judge said Ritz and Mucci could both testify before a jury.
Monsanto faces 5,000 lawsuits nationwide alleging Roundup caused cancer, mainly in state courts. Farmers in California have been using the weed killer on more than 200 types of crops.
But serious doubts remain as the World Health Organization in 2015 classified glyphosate as "probably carcinogenic to humans". Homeowners, meanwhile, used Monsanto Roundup on their lawns and gardens.
A California man dying of cancer makes his case to a jury on Monday in a trial against agrochemical giant Monsanto that could have sweeping ramifications, news agency AFP reported. "Here, although there is no need to specify precisely the circumstances under which each plaintiff was exposed to glyphosate, only evidence supporting the conclusion that glyphosate causes National Hockey League in doses within the realistic realm of actual human exposure can get the plaintiffs past summary judgment".