The first evaluation of the Community Return Programme — introduced in October 2011 to ease overcrowding — found that 548 (72%) of the 761 participants had successfully completed the programme.
A further 108 (14%) were currently in the programme, while 88 (12%) were in breach of it and returned to prison.
The programme— described by the report as unique in the world — combines unpaid work for the benefit of the community with early, supervised release and resettlement support.
Prisoners serving sentences of between one and eight years can apply, once they have served half their sentences and are deemed suitable — based on their behaviour, risk to the community and other criteria.
An evaluation report, covering the period October 2011 to December 2013, by the Irish Prison Service and the Probation Service, found that 302 offenders (40%) were drug dealers, 119 (16%) were in for assault and threats and 76 (10%) were convicted of theft.
A significant number were in for serious offences such as robbery (9%) and burglary (8%), as well as smaller numbers for weapons (3%).
There were seven kidnappers and two killers included.
The average sentence length was three years, with 10% serving six years or more.
Almost four in 10 participants were in the two open prisons (Loughan and Shelton), with the next biggest numbers coming from Mountjoy, Limerick, Midlands, Training Unit and Cork prisons.
Of the 761 offenders, 329 were from Dublin and 245 were from Munster — 155 of whom were from Cork or Limerick.
The report said the participants carried out a wide variety of work, including gardening, painting and renovation, benefiting community groups such as charities, sports clubs, schools, and services for the homeless.
It said prisoners are given structure and routine on the programme and develop a work ethic, self-esteem and work skills. For some, it helped them stay out of trouble, it said.
The 201,056 hours of unpaid work completed translated to €1.7m-worth of work, based on the minimum wage, the report said.
It said there are “a significant number” of prisoners on temporary (unstructured) release, separate from the programme.
Official figures show there were 400 such people on November 3.
It said this number could be reduced, as there was capacity in the programme.
The report said changes would need to be made, such as allowing prisoners to apply before they serve half of their sentence.