David Strang has been speaking during Scotland's Prisons Week, which highlights the needs of victims, inmates and staff.
He said that more intervention needs to be done to stop at-risk people from entering prisons in the first place.
The prison system has hit the headlines a number of times over the past few weeks:
The Prisoner Officer's Association recently staged an illegal walkout across the country over staff cuts and rising prison violence.
A killing recently happened at Pentonville jail in one incident and two inmates escaped from the prison weeks later.
A riot causing around one million pound's worth of damage also happened at Bedford prison.
Speaking on Premier's Inspirational Breakfast, David Strang said: "Within two years, two-thirds of people who leave prison are reconvicted.
"We need to have more emphasis on rehabilitation, making sure that when people leave prison they've got somewhere to stay; I know of people who leave prison and don't know where they're going to sleep that night.
"I think there should be more investment in prevention in the first place... support for people who've perhaps been excluded from school or are in danger of offending.
"We should be investing in them to make sure their lives turn out better."
Listen to Premier's Rosie Wright and John Pantry speaking to David Strang on Inspirational Breakfast: