Mr Groser was told to reconsider his response to six of the eight categories of information.
"When the Minister reconsiders his decision he will be required to do so in a way that is consistent with his obligations under the Act."
The ruling could also have implications for the Ombudsman's office, which upheld Mr Groser's decision not to release the documents.
Justice Collins said he made the order for two reasons.
Firstly, there was "no lawful basis" for the Minister to withhold some of the information requested by Professor Kelsey.
Secondly, Justice Collins wrote, "the Act plays a significant role in New Zealand's constitutional and democratic arrangements".
"It is essential the Act's meaning and purpose is fully honoured by those required to consider the release of official information."
Professor Kelsey said her decision to seek a judicial review had been vindicated.
"The Minister's approach epitomises the contempt for democratic processes and accountability that has pervaded these negotiations," she said in a statement.
But a six month deadline imposed by the court for further orders was "cold comfort" because it would fall after the negotiations had been completed.
"[Mr Groser's] unlawful approach in circumventing the Official Information Act appears to have achieved its goal," Professor Kelsey said.