Real IRA leader Michael McKevitt has been refused permission to bring his appeal against his conviction for directing terrorism to the Supreme Court.
The 64-year-old was the first person in the history of the state to be convicted of such an offence.
In 2003, Mr McKevitt was convicted of directing terrorist activities.
A civil court in Belfast subsequently found him liable for the 1998 Omagh car bomb that killed 29 people.
The Real IRA leader has tried to appeal both rulings, but without success.
This latest attempt to overturn his criminal conviction for directing terrorism in part centres around the use of section 29 search warrants - which were deemed unconstituional many years after his case was determined.
His lawyers claimed this could be considered a newly discovered fact for the purpose of a miscarriage of justice application.
They say the point is so important it should be decided by the Supreme Court, but that route has now been blocked by the Court of Criminal Appeal which has called McKevitt's application "misconceived".