Cr Bryan Scott resigned today and said the council's meeting on Wednesday was his last.
In an email to councillors, he said the "key policy" that he stood for at the last election was to achieve a "fit for purpose" Land and Water Plan.
"Clearly this is no longer possible for the foreseeable future due to the recent government decision to block plan notification.
"It appears that government has an agenda to go back to the bad old days of justifying environmental degradation in the name of economics.
"I will take no part in this."
Notifying the council's land and water plan at this week's meeting would have been an important line in the sand, Cr Scott said.
The last-minute intervention by the government had been "gutting".
He said despite some agreement behind the scenes, the council had slipped into two polarised camps for votes.
But at Wednesday's meeting Cr Scott said what he needed to say and shook every councillor's hand.
He said he understood that with less than a year until the next election his decision to leave would not trigger a by-election.
"I wish our Community and Environment well from the bottom of my heart."
