The "three strikes and you're out" Bill, put forward by Act New Zealand MP David Garrett aimed to keep career criminals in prison after their third violent offence, Sensible Sentencing Trust spokesman Garth McVicar said.
Current legislation did not see offenders given maximum sentences for repeat violent crimes, he said.
The move to support the Bill was made by victims at the fifth annual conference of the Sensible Sentencing Trust in Taupo at the weekend.
Under the proposed Bill, after a person's third violent offence a judge would have no option but to give a mandatory sentence of 25 years.
"It's ridiculous that an offender's slate is wiped clean after their sentence ends and there is no added penalty down the track if they reoffend, which as we all know, they mostly do."
In addition to supporting the Bill, those attending the conference also wanted the Government to commit to ending concurrent sentencing, making life mean life, and work toward ending all parole before the end of an offender's sentence.
They called for an end to the legal right of defendants to remain silent in court, the right to rebut false defence claims in court, a mandatory national protocol for including victims in court proceedings and an end to lengthy delays.
"This may seem like a big ask, but all of these people have lost someone dear to them in the most brutal way, and then have gone looking for justice in a place we call the justice system and been bitterly disappointed. In that context, these demands are entirely reasonable."
The justice pendulum had "swung too far in the direction of the criminals", he said.
Police Minister Judith Collins told the conference the Government was already clamping down on criminals with new legislation.
"Law-abiding New Zealanders are sick and tired of seeing their rights eroded and, in many cases, ignored in favour of the rights of criminals. This Government is not standing for that."
