The Court of Criminal Appeal has increased the sentence imposed on Ian Horgan for the manslaughter and rape of beautician Rachel Kiely in October 2000.
At his retrial in March 2006, Mr Justice Barry White sentenced Horgan to eight years in jail, but suspended the last six.
Horgan was due for release in September this year.
The Court of Criminal Appeal ruled that Mr Justice White had made an error in principle and ruled the sentence should be increased to 12 years.
The sentence will be backdated to September 2001, when Horgan was first taken into custody. With remission, that means he is likely to be released in 2010.
Horgan was convicted of Rachel Kiely's rape and murder at his first trial in 2002, a conviction that was overturned by the Court of Criminal Appeal.
At his second trial, the State Pathologist, Dr John Harbison, was no longer available to give evidence and Prof Marie Cassidy had to give evidence based on photographs.
Rachel Kiely's family said they were disappointed at the sentence imposed by Mr Justice White, but they say they are delighted at the court's ruling today.
The Court of Criminal Appeal will give its reasons for the decision at a later date.
