Director of Public Prosecutions Claire Loftus said the directive will give victims the right to receive reasons in a range of offences – including rape, child sexual abuse and harassment.
The ruling must be transposed into Irish Law by November 2015.
Currently, the DPP’s office only gives reasons for not prosecuting in cases involving fatalities.
The directive will also provide victims of serious crime the right to a review of a decision not to prosecute.
Speaking at a conference in Dublin, she also urged counselling organisations to co-operate with her office in the disclosure of information in relation to criminal prosecutions.
She said some organisations take the view that even where victims have given consent, those who provided counselling can decide what material should not be handed over.
Ms Loftus said all that material is eventually handed over but often at the last minute when trials are about to commence which is very unsatisfactory.
She said that the HSE, Dublin Rape Crisis Centre, One in Four and Cork Sexual Violence Centre have all signed Memorandums of Agreement with the DPP’s office which provide for disclosure of information.
Ms Loftus said these agreements reduce delays and consequent trauma to victims caused by late adjournments because cases are not ready.
She added that the new Court of Appeal – which she understands will have a permanent criminal division – will undoubtedly relieve the situation in appeals against conviction or sentence and prosecution applications for reviews of sentences.