Minister for Justice Dermot Ahern has said the Criminal Procedure Bill will take effect immediately.
Mr Ahern said the Bill, which has been signed into law, allows for exceptions to the double jeopardy rule.
Someone who has committed a very serious offence can now be retried if there is new and compelling evidence brought forward, subject to court approval.
It also allows for victim impact statements to be read out in court, in a wider variety of cases from murders to harassment. The new law is not retrospective.
Mr Ahern said the bill 'provides, for the first time, for retrials following acquittals if new and compelling evidence emerges, or where the first trial was tainted by an issue such as perjury or intimidation.
'There would also be provision for a retrial where the judge at the first trial erred in law by, for example, excluding certain evidence.'
Meanwhile, the Minister said the new prison at Thornton Hall is not being scrapped in the Budget.
However, he said that a number of other prison spaces will be built in different locations across the country because a medium-term solution is needed.
