Green Party MP Keith Locke has announced he will retire at this year's election.
Mr Locke, 66, said it was time to move on to new projects, but that he would be working hard until the election.
"The National Government can't relax just yet," he said.
"I will keep up the political pace right through to the election. The Search and Surveillance Bill and the SIS Amendment Bill will not have an easy ride through Parliament, and I will keep campaigning for my Bill of Rights Amendment Bill as well as for the withdrawal of SAS troops from Afghanistan."
Among his post-Parliament projects, Mr Locke said he would be writing political history - including that of the Green Party - and engaging more with global environmental organisations.
"Even when I am not operating from a parliamentary platform, those who start wars and abuse human rights will not escape my attention."
Mr Locke, who has been in Parliament since 1999, said he was particularly proud of his achievements as a human rights watchdog and peace advocate.
"Perhaps my efforts mean that our anti-terrorism and security laws are not so draconian as they are in some other western countries," he said.
"Throughout my term I've tried to steer New Zealand foreign policy in a more independent direction, less tied to American interests. Successes of which I was a part include getting rid of our air combat force, staying out of the Iraq war, and New Zealand playing a leading role in a treaty to ban cluster bombs.
"I've been honoured to be a parliamentary spokesperson for those suffering human rights abuses in China, Burma, Palestine, Tonga and many other places."
