Nathalie Matthews, 38, is applying for a private apprehended violence order to protect her from the former federal Labor leader, who she accused of emotional and physical abuse.
Apprehended violence orders can be taken out by police or private citizens, as Ms Matthews has opted to do.
Mr Latham - who is an independent in the NSW upper house - denied the allegations and has not been charged with criminal wrongdoing.
The 65-year-old is set to fight the order during a three-day hearing in Sydney's Downing Centre Local Court on Wednesday.
He will call two witnesses and play video evidence in support of his argument while Ms Matthews will call one witness, the court was previously told.
The independent MP previously sought to subpoena the billionaire founder of WiseTech Global, Richard White, but that move was abandoned in September.
The local court refused to release court documents detailing allegations against Mr Latham, which are not the subject of criminal charges and remain untested.
The hearing comes nearly seven months after he claimed the AVO application had been withdrawn in a social media post.
"I was due in the Sydney Local Court tomorrow for the latest instalment in the private AVO application against me," he wrote on X in October.
"But it has now been delisted and the application withdrawn … that's the end of that."
Instead of the neat ending he envisaged months ago, Mr Latham and his former partner will air their dirty laundry in court.
The controversial politician has served as a right-wing independent MP since 2023, when a falling out with Senator Pauline Hanson led to his departure as One Nation NSW leader.
He led the populist party's return to state politics in 2019, 15 years after his failed attempt to lead Labor to federal election victory.
After losing to incumbent prime minister John Howard in 2004, Mr Latham resigned from federal parliament and was later ejected from the Labor party.
He has been embroiled in several scandals during the past year, including taking photos of female MPs without their knowledge, for which he has apologised.
1800 RESPECT (1800 737 732)
Lifeline 13 11 14
Men's Referral Service 1300 766 491
National Sexual Abuse and Redress Support Service 1800 211 028
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