Howard League for Penal Reform spokesman Jarrod Gilbert said it was a brave move based on robust evidence instead of fear and populism.
He had some reservations about whether the goal of a 25 per cent reduction could be reached but welcomed the Government's shift in rhetoric away from "zero-tolerance".
Corrections chief executive Ray Smith said the $65 million reprioritisation would be funded by a restructure of the department - which was underway - and through the closure of several older prisons.
More savings would be made from the proposed combination of the department's prison, rehabilitation and probation arms, which would cut 140 middle-management jobs.
Rethinking Crime and Punishment spokesman Kim Workman supported the changes but said they would be difficult to achieve given the "very high imprisonment rate" in New Zealand.
One of the most dramatic proposals in the pre-Budget announcement was the expansion of drug and alcohol treatment to 33,000 more people in prison and in the community.
What is proposed?
* 25 per cent reduction in reoffending by 2017
* 18,500 fewer victims of crime
* 600 fewer people in jail, and 4000 fewer community offenders
How will it be achieved?
* 500 per cent increase in drug and alcohol treatment for criminals
* 230 per cent increase in rehabilitation services
* 30 per cent increase in education and job training
* More support for prisoners to find jobs, new partnerships with employers and iwi
What is the cost?
* $65 million, all from within the Corrections Department. Up to 140 jobs will be trimmed, some older prisons will be closed and others downsized