Minister for Justice Michael McDowell has signed the order bringing the Criminal Justice Act 2007 into force.
The Act provides for stiffer sentences for repeat offenders, changes to the bail laws and the right to silence, and longer detention periods for some suspects.
Mr McDowell said that the new measures would put gardaí and the courts in a stronger position to deal with the threat from gangland crime.
While the Act has been criticised by civil liberties groups, the Minister repeated his view yesterday that it was "reasonable and proportionate" and contained numerous safeguards.
"The new Act, taken together with legislative changes made last year in relation to, for example, the admissibility of witness statements, will go a long way towards redressing the balance in favour of law-abiding communities who are threatened daily by gangland activity."
Mr McDowell said he was disappointed not to have had more support from the Opposition on the Act. Further anti-crime measures would be drawn up, including the creation of a DNA database, for which Government approval had been obtained.
One of the last pieces of legislation to pass through the 29th Dáil, the Act was signed into law by President McAleese earlier this month. Mrs McAleese had earlier convened a meeting of the Council of State to examine the constitutionality of the Act.
A number of the measures come into immediate effect while others, in particular the changes proposed to the right to silence, take effect from July 1st.
Mr McDowell made no order yesterday in relation to provisions in the Act for the electronic tagging of offenders and his spokeswoman was unable to say when these would come into effect.
Under the Act, repeat offenders will face mandatory minimum sentences of up to 10 years where their original offence attracted a sentence of five years or more unless the court considers the sentence disproportionate. The provision applies to murder, firearms, drugs and other serious offences. Post-release supervision orders may also be applied to those jailed for serious crimes.
The Act changes the right to silence by allowing the court to draw inferences from an accused person's failure to account for certain facts while being questioned. Corroboration is required from other evidence and a person cannot be convicted on an inference alone. The seven-day detention period is being widened and now embraces murder, firearms and kidnapping cases.
Applicants for bail will have to provide information about their means, their previous criminal record and any offences committed while previously on bail. The prosecuting authorities are being given the right to appeal against decisions to grant bail.
