Andrew Little says if Labour wins the election, it will make sure victims are always notified when a mentally unwell offender is allowed out of care.
If offenders are detained in a hospital or mental health facility in relation to their crime, the victims will be notified when they are allowed for the first time on unescorted leave or overnight unescorted leave, but not if they are out on escorted leave.
This allows the possibility for unsuspecting victims to stumble upon the offender out in public.
This loophole came to light last month when Christie Marceau's killer was allowed out of care without Marceau' parents being notified.
Brian and Tracey Marceau were unaware murderer Akshay Chand had been granted leave until they were informed by the media. He had been seen at an Auckland public library and at McDonald's and Countdown, Fairfax reported.
Tracey Marceau said it was "another kick in the face".
Victim Advocate Graeme Moyle said he had been asking the Government about the legislation for some time now, and was recently told by Little that Labour would change the situation.
Little confirmed to the Herald Labour would make the move, saying the victims should be told of any release or change in management that meant the perpetrator could be in public places.
"The reality is that there's a dead person with a grieving family and they're entitled to know that the person who's caused the family member's death has been [let out]," he said.
While it was important for the offender's "basic human rights" to be respected, it was "just as important that the family are able to manage their situation and their grief".
"They shouldn't be left surprised if they stumble upon the person who has caused the death of their family member."
While he was focusing on the loved ones of murder victims, Little said any victims of crimes committed by the mentally unwell should be notified.
Minister of Justice Amy Adams said in a statement a person allowed out on escorted leave is not being transitioned into the community, "so there is no requirement under the law for notification".
However she said she was "happy to consider whether any change to this is justified and necessary".
Act leader David Seymour was in support of the change, saying it didn't "sound like a bad idea on the face of it".
"Certainly there's been cases around New Zealand where people have had a person that's severely victimised [them] released and not known about it," he said.
"Ultimately, do we have justice purely for the welfare of the victims or for the welfare of the offenders?"
He said Act's position was to prioritise the rights of victims.
Maori Party co-leader Marama Fox said they would "absolutely" support such a change as well.
"What if they [the victims] are just walking around and are suddenly confronted with the person who perpetrated a crime against them?"
Fox said people needed to be able to "build themselves up" to prepare for that happening.
She said it was "just cruel" to put victims at risk of coming across the offender unexpectedly.