Former press secretary Rachel MacGregor has filed a lawsuit against Colin Craig.
The Herald can reveal that MacGregor is counter-suing Craig and filed papers in the High Court at Auckland today.
It is understood those papers have been served on Craig, although he declined to comment to the Herald tonight.
The former Conservative Party leader filed defamation proceedings against her in November 2016.
MacGregor was never served and only learned of Craig's legal move through media this week.
As a result, she has taken her own legal action.
"When media alerted me that Mr Craig had sued me I sought legal advice," she told the Herald tonight.
"That advice was that I needed to file a document by today in order to protect my legal position.
"I will not be commenting further at this stage as the matter is before the court."
MacGregor resigned two days before the election in 2014, and made a sexual harassment complaint against Craig.
She later received an out-of-court settlement.
Craig is currently suing Whale Oil blogger Cameron Slater for allegedly defaming him in posts about sexual allegations involving MacGregor.
The case was heard at the High Court at Auckland, with the judge's decision still reserved.
Slater is counter-suing Craig for defamation over claims made in a booklet called Dirty Politics, which was distributed to 1.6 million homes.
Last week Radio New Zealand reported that Craig was planning to sue MacGregor for defamation if he lost the case against Whale Oil.
But Craig denied that report to the Herald, saying he had "historically" considered suing MacGregor but decided against it.
In response MacGregor said she had been advised that Craig's "failure" to serve those proceedings on her or her lawyers for several months was a breach of the High Court rules.
"It is unclear to me why Mr Craig would want to file proceedings but not give me notice of them.
"I strongly believe Mr Craig's claim against me is an abuse of process.
"Over the last year I have been dragged unwillingly into being a witness in two court proceedings by Mr Craig and others.
"I have been required to give evidence that was both highly personal and highly distressing.
"I would like to get on with my life."
MacGregor invited Craig to "put an end" to the saga by withdrawing the proceedings.
Craig confirmed to the Herald that defamation papers had been filed last November, but would not say whether they had been served to MacGregor, whether it was an abuse of process, and whether he planned to withdraw the defamation suit as requested.
"My standing rule, and I'm not going to break it, is that on legal matters I never comment till the judgment is out," he said. "I don't comment on any legal issues until they are ultimately at an end."