Colin Craig is to give evidence at his defamation trial in the High Court at Auckland this afternoon.
The former Conservative Party leader is accused of defaming Taxpayers' Union director Jordan Williams.
Williams alleges Craig defamed him at a press conference, and then again in a pamphlet the former politician paid to have published and distributed to more than 1.6 million New Zealand households.
The allegation that Williams lied came after he took information given to him by Craig's former press secretary Rachel MacGregor to other Conservative Party members.
MacGregor had alleged Craig had sexually harassed her and Williams felt obligated to warn the other party members, despite her telling him not to disclose the information.
His aim at the trial, the result of a civil defamation case Williams brought against Craig, is to prove the information he shared about the then-leader was the truth and that he did not lie.
Colin Craig defamation trial: everything you need to know so far
Colin Craig whistle blower's motive questioned at defamation trial
Former Conservative Party leader Colin Craig's letter to press secretary: 'Love you Rach oooox"
Rachel MacGregor on Colin Craig - in her own words
Craig has been seated in the public gallery for the first eight days of the trial, before Justice Sarah Katz and a jury.
But this afternoon he will move to the witness box and read his evidence.
At 2.15pm Craig's lawyer Stephen Mills QC will open his case, explaining to the jury Craig's defence.
Then Craig will read his brief, which is expected to take at least an hour-and-a-half.
Craig will then be cross-examined by Williams' lawyer Peter McKnight.
McKnight closed his case this morning on day nine of the trial, which is set down for five weeks.