In a breakthrough victory, the Land and Environment court today ruled the NSW Government's land-clearing laws were made unlawfully, and were therefore invalid.

The Nature Conservation Council fought the legislation made by the Berejiklian Government, which had permitted private landholders to carry out large-scale clearing of native vegetation without prior approval or environmental assessment.

CEO Kate Smolski said the government "bungled" the introduction of Native Vegetation Code 2017, claiming the process "demonstrates its careless disregard for nature in NSW".

"Today's ruling is an embarrassing admission of failure by the Berejiklian Government and a great victory for the rule of law and the thousands of people who have supported us in taking this action," Ms Smolski said.

"Premier Berejiklian must act now to prevent further plundering of our forests, woodlands and water supplies by scrapping these laws and making new ones that actually protect the environment."

The conservation group argued in court that the codes were invalid because, contrary to legal requirements, Primary Industries Minister Niall Blair did not reach an agreement with Environment Minister Gabrielle Upton before making the codes last August.

A spokeswoman from the office of Minister for Primary Industries said the NSW Government was "moving quickly to respond to (the) court's declaration".

"Its top priority is providing legal and operational certainty to ensure the benefits of the reform continue to be realised".

The statement said the government was "absolutely committed to delivering on this important reform and meeting its obligation to act on the recommendations of the Independent Panel".

Action by the conservationists was launched last November, legally represented by the Environmental Defenders Office.