Brian Dobbs helped to establish the Conservative Party in 2011.
He said this afternoon that his resignation, effective immediately, was a result of "recent revelations and the events of the last week", which had made it untenable for him to stay on as a member.
"It is with great sadness that I do this as I know there is a strong conservative movement within New Zealand that desperately needs representation and a voice in Parliament. As demonstrated by the 140,000 voters gained in the last election whom resonated with the policies that are democratic, moral, social and fiscal conservativism.
"I would like to thank the people I have worked most closely with in helping form and operate the Conservative Party.
"However, due to some recent revelations and the events of the last week it has become untenable for me to remain a member and the chairman."
Mr Dobbs was the eighth board member to resign this week, following Colin Craig's admission of inappropriate conduct in relation to his former press secretary, Rachael MacGregor.
Just two members remain, meaning that the board is likely to dissolve altogether. They are John Stringer and Laurence Day, who are both critics of Mr Craig.
The depleted board had been scheduled to meet tomorrow in Auckland. But because Mr Day is overseas, it will not be able to get a quorum. That meant one of the motions tabled for the meeting, to cancel Mr Craig's membership, could not be passed.
Mr Dobbs said earlier this week that all of the allegations against Mr Craig should be fully investigated, and if he was cleared he should be given a second chance.
Now that he has departed, this leadership review is in limbo.
Mr Dobbs ran in the Waikato electorate in the general election, winning 1442 votes and placing fourth.
Seven board members resigned on Tuesday after Mr Craig admitted his inappropriate actions in a news conference the previous day.
Former deputy leader Christine Rankin, who was the first to resign, said Mr Craig had set himself up as "squeaky clean" and his admissions had completely undermined the morally conservative party,
The finer details of Mr Craig's inappropriate interaction with Ms MacGregor are suppressed by a confidentiality agreement.
Despite both parties expressing a wish to waive confidentiality, the agreement remains in place.
