Based on the Nottingham Declaration, the Essex version pledges both authorities to actively tackle climate change by working together and with other partners and their local communities.
Uttlesford DC leader Mark Gayler said:
'It's a landmark day for both councils as we publicly declare our intentions to become the environmental guardians of our respective areas of north Essex.
'The future of our environment is dependent on partners working together to ensure the well being of our district. We will do everything we can to reduce greenhouse gas emissions and will vigorously fight anyone or anything that compromises that.
'It is equally exciting to find ourselves working closer with our neighbour Braintree District Council. I am sure we will both learn much as we work together.'
Braintree DC leader Graham Butland said:
'We used to ask about the financial implications of all our decisions, but now we shall want to know about the environmental impact of decisions made by the council. This signing is just the beginning, and while both councils already have a commendable record of practical energy improvements, there is still a long way to go.'