Prison officials say that is an extra year compared to 2008, and three and a half years more than in 2004.
The number of people serving life sentences continues to rise in the prison system due to the longer sentences being served.
At the end of 2011, there were 290 people in custody serving a life sentence. This compares to 264 people in 2007 and 221 in 2004.
A prison service official said that 22 people were sentenced to life in 2011 — 21 for murder and one for a sexual offence — compared to 18 people in 2010.
He said there were 67 life sentence prisoners under supervision by the Probation Service in the community after being released.
On the issue of how long life sentence inmates serve behind bars, the official said: “The average time spend in custody by these persons was 17.5 years.”
He said the duration had increased substantially over recent decades.
“During the time period 2004 to Dec 31, 2008, the average time spent in custody by life sentence prisoners over this period is 16.5 years. This compares to an average of just over 7.5 years for releases dating from 1975 to 1984, just under 12 years for the period dating from 1985 to 1994 and just under 14 years for the period dating from 1995 to 2004.”
The official said that as of Jul 31, there were 67 life sentence prisoners under supervision in the community.
Life sentences are mandatory in cases of murder and can also be imposed for a number of serious crimes, including some sexual offences.
During his term as justice minister, between 2002 and 2007, Michael McDowell, instigated a policy through the Parole Board of substantially increasing the custodial terms of life sentences.
Advocates for Victims of Homicide called for mandatory life sentences for murder to be reviewed to allow judges set sentence tariffs — such as 25 years for murder in the first degree.
The support group said killers should have to serve 15 years before they can even be considered for parole, almost twice the current threshold of seven years. They also said the Parole Board should seek written representation from the family of the victim when reviewing the case of someone convicted of homicide.
People sentenced to life this year include:
* Gary Howard, 24, given two life sentences for the murders of Patrick Mooney and Brendan Molyneaux in Pearse House Flats in Jan 2010.
* Wayne Kinsella, 40, given a life sentence for the murder of Adil Essalhi in Blanchardstown in Jan 2011.
* Martin Morgan, 21, led a gang that kicked Polish man Lukasz Rzeszutko to death in Coolock, north Dublin, in Oct 2010.
* Barry Doyle, 26, murdered Limerick man Shane Geoghegan, in a case of mistaken identity, in Nov 2008.