Studies on the toxicity of weedkiller, known as glyphosate, must be disclosed by the European Food Safety Agency (EFSA), EU judges ruled on Thursday.
It comes following campaigns for it to be banned.
Concerns about its safety were highlighted when a World Health Organization agency concluded in 2015 that it probably causes cancer.
The European Court of Justice said it was in the public interest to access the information on glyphosate, related not only to knowing what is or could be released into the environment but to understanding the impact of the emissions the weedkiller releases.
The judges annulled two decisions by the EFSA that had denied people access to the information on it.
The two cases were brought by Green members of the European Parliament among others.
Responding to the ruling, Corporate Europe Observatory’s agri-business researcher, Martin Pigeon, said: "This ruling is very important as it confirms the Court's case law on the overriding public interest in public access to all toxicity study data for pesticides.
"The ruling extends this disclosure requirement to the sections on ‘material, experimental conditions and methods’ as well as ‘results and discussion.
“So today’s ruling provides EFSA with a straightforward legal guideline for dealing with future disclosure requests: Names and signatures of individuals aside, studies must be disclosed in their entirety," he added.
A spokesperson from the EFSA said in a statement the decision was welcome. "This case, and the court's ruling, is important because it provides orientation for EFSA and others charged with interpreting EU legislation on public access to documents."