Criminal law, traffic matters, DUI, assault, theft, fraud
A previous conviction in Victoria or anywhere in the world for that matter is admissible in court for the purposes of sentencing.
Before the hearing, police would have checked the other Australian jurisdictions and New Zealand for prior convictions. The obligation is on the police prosecutor to put any convictions before the court.
If for some reason your Victorian conviction is overlooked, you have no obligation to declare it.
Having said that, if you are represented by a lawyer, you should tell the lawyer about the Victorian conviction so they can better prepare their sentencing submission and so they are not caught by surprise.