John Gilligan, who was convicted for drug trafficking, may walk free from Portlaoise prison anytime after midnight tonight.
The 61-year-old, who was an adversary of murdered journalist Veronica Guerin, has already told media outlets not to expect an interview.
Gilligan is being released as Jessbrook, the stud farm in Co Kildare once controlled by him and his wife Geraldine, is on the market, having been seized by the Criminal Assets Bureau.
While speculation is widespread about the timing and manner of his release, the Irish Prison Service said it would not comment on individual cases.
However, it is understood the service is reluctant to make any special arrangements for Gilligan, who was initially given a 28-year sentence in March 2001 which was reduced by eight years on appeal in 2003. He is being released this week as he is entitled to remission.
Sources said that technically Gilligan would be a free man from midnight but criminals were rarely released at this hour. Prisoners were usually released any time after breakfast which takes place from about 7.30am, a source said.
Last week, Gilligan issued a statement through his legal advisers saying he would not grant interviews even if the media were prepared to pay sums of €1 million for access to him.
A large number of reporters and photographers are nevertheless expected to gather at the prison in advance of his release.
Gilligan, who has denied the murder of Ms Guerin, brought several legal challenges to his detention while his family contested the confiscation by the Criminal Assets Bureau of Jessbrook and other properties. All challenges were finally dismissed last year.
