The major spend is to ensure the prison is in good condition and fit for its purpose, and to improve security and safety.
The upgrade will also increase opportunities for prisoners to work and train for employment while in prison.
Prisoners' Aid Rehabilitation Society (Pars) regional manager Steve Treloar, based in Wanganui, said yesterday that any skills a prisoner learned in prison set them up for release.
Over the years, Mr Treloar has seen a huge increase in Release to Work compared to 20 years ago when there was nothing.
"In the Release to Work they earn money, and when they leave prison they can set themselves up. Without the pressure and stress they will never reoffend."
Under the Release to Work programme, five prisoners are working as labourers on the administration building upgrade at the prison.
Corrections Minister Anne Tolley said educating and rehabilitating prisoners to avoid reoffending was a big priority.
"If we can provide opportunities to help them turn their lives around to stop them from reoffending, we can make communities safer and prevent the taxpayer having to foot the $100,000 a year it costs to keep a prisoner locked up."
Prisoner employment contributes to Corrections' target to reduce reoffending by 25 per cent by 2017. Whanganui Prison has trade training opportunities including pre-cast concrete, timber joinery and processing, horticulture, food preparation and catering and grounds maintenance.
The two wings will undergo a general internal refurbishment, security upgrades, earthquake strengthening, upgrading prisoners' showers, and building secure staff bases.
Additionally, the east wing will have new exercise yards built, and cell hardening to meet high-security classification requirements.
The upgrade is part of an $81.5 million programme of capital works in five prisons from 2013-2017. As well as Whanganui Prison, the programme involves the development, upgrade and refurbishment of facilities at Waikeria, Tongariro/Rangipo, Rolleston (almost complete) and Invercargill prisons. Whanganui Prison can hold up to 538 male prisoners with security ratings ranging from minimum to high. The oldest part of the prison, the main Kaitoke prison complex, was built in 1978 while a self-care unit and minimum security units opened in 2005.