The Government is getting tougher on repeat violent criminals as National and ACT parties have announced an agreement on a three-strike policy today.

The policy, announced by Prime Minister John Key, ACT leader Rodney Hide and Police and Corrections Minister Judith Collins, will be incorporated into the Sentencing and Parole Reform Bill, ensuring repeat criminals get the maximum allowable sentence.

If passed into law, an offender would receive a standard sentence and warning for the first offence, a possible jail sentence with a second sentence, and with a third offence he or she would receive the maximum penalty in prison for that offence, rather than a life sentence with a minimum period of imprisonment of 25 years as originally proposed.

The court can still decide not to order the maximum sentence be served without parole if found unjust. The policy would only apply to offenders aged 18 years and over.

"National and ACT are determined to hold serious repeat offenders to account, improve public safety, provide a greater measure of justice and closure for victims and maintain the confidence of the public in the justice system," Ms Collins said.

"The regime will be harsh - but only for the small number of people in our community who show continued disregard for the law and contempt for society."

Mr Hide said the policy sends a clear message that repeat violent offences won't be tolerated.

"It is about making our homes, our businesses, and our communities safe once more."