David Southwick divulged details of the surreptitious recording to the Federal Court on Wednesday in Moira Deeming's defamation trial against Victorian Opposition Leader John Pesutto.
Ms Deeming claims Mr Pesutto defamed her by suggesting or implying she was a Nazi in comments he made following the Let Women Speak rally.
The March 2023 event was gatecrashed by neo-Nazis who performed the Nazi salute on the steps of state parliament.
Mr Pesutto has denied any wrongdoing.
Earlier in the trial, it was revealed Mr Southwick secretly recorded a meeting held between Ms Deeming and Liberal leadership the day after the rally.
In the 70-minute recording played to the court, Ms Deeming was criticised for her involvement in the rally and for photos showing her having champagne afterwards with fellow organisers.
Moira Deeming's barrister Sue Chrysanthou grilled the deputy leader about his secret recording. (James Ross/AAP PHOTOS)
She is also heard telling the leadership she did not realise the Nazis were even at the rally and she did not support them.
Ms Deeming's barrister Sue Chrysanthou SC grilled Mr Southwick on Wednesday morning as to why he surreptitiously created the recording.
He told the court he felt he could not trust Ms Deeming and he needed to protect himself and the Liberal Party from what was about to happen.
"I wanted to make sure the whole events weren't turned around and misconstrued," Mr Southwick told the court.
"For me, it was an insurance policy."
David Southwick said he hoped his tape of the meeting would never have to be used. (Joel Carrett/AAP PHOTOS)
The recording was uncovered a week before the trial started and Mr Southwick maintained he never intended for anyone to hear it.
The other members of the meeting did not know he was recording it on his iPhone, Mr Southwick said.
"I hoped that tape would never have to be used," he told the court.
"That's why I didn't talk about the tape or mention it to my colleagues."
His evidence continues.
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