Colm Murphy has been jailed for 14 years by the Special Criminal Court in Dublin for his role in the Omagh bombing which killed 29 people, including a woman pregnant with twins, and injured more than 300 in 1998.
He was the first person to be convicted in either the Republic or Northern Ireland in connection with the "Real IRA" bombing, the worst terrorist atrocity in the 30 years of the Troubles.
Jailing him for 14 years, to date from his conviction last Tuesday, Mr Justice Barr, presiding, said: "The court has an important duty to make it abundantly clear to other extremists, by its sentence, that such criminal activity will be treated with the utmost severity and huge sentences may be expected."
Murphy showed no emotion as the sentence was handed down and he turned and waved to his relatives after sentencing.
Relatives of 17 of the Omagh victims were in court for the sentencing and they applauded as Murphy was led from the dock to the cells below.
Mr Justice Barr said that Murphy had been "a service provider" for those who had planned and carried out the Omagh bombing.
The judge said Murphy was "a long-time republican extremist and member of a dissident group which is opposed to the peace process in Northern Ireland". He had been convicted of criminal complicity in the bomb which exploded in Omagh on August 15th, 1998, resulting in major loss of life, personal injury and damage to property.
It had been established beyond doubt that his part in the operation,which he knew involved the movement of a bomb to Northern Ireland for detonation, consisted of the provision of two mobile phones which were used by the bombers.
There was no evidence to connect the accused with the bomb itself, the planning of it or any other organisation of the attack. The court accepted that Murphy probably did not intend to cause death.
But a powerful bomb was used at Omagh as had been used earlier at Banbridge and those who participated must have realised that the planting and detonating of such a bomb was fraught with danger. The perpetrators of the crime, including the accused, had no regard for the right to life and had shown a disregard for basic human rights of others.
The judge said that the court would have sentenced Murphy to the maximum term of imprisonment allowed under the law if he had been convicted of being a planner or maker of the bomb. Murphy was a "service-provider" and was guilty of complicity in the crime.
The court accepted that there were significant distinctions between the bomb-planners and service-providers such as the accused, but all were guilty of a major crime.
The maximum prison sentence which could be imposed was 20 years and taking into account all the facts, the court sentenced Murphy to 14 years, the judge added.
Following sentence, the court refused leave to appeal following an application by Murphy's counsel, Mr Michael O'Higgins SC, who set out 38 grounds of appeal.
Mr O'Higgins said after the hearing that his client would be appealing to the Court of Criminal Appeal.
Det Supt Tadhg Foley, the officer who led the Garda investigation into the Omagh bomb, told the court yesterday that Murphy had become involved in the criminal conspiracy in late July or early August 1998.
He had lent his phone for a bomb attack in Banbridge which caused extensive damage to property and injured police officers who had been evacuating the area. He agreed with Mr Peter Charleton SC, prosecuting, that Murphy would have been aware of that when he lent his phone for another attack which turned out to be in Omagh.
Murphy gave assistance to the gardaí by naming names in relation to the incident.
In a plea of mitigation, Mr O'Higgins said that while his client recognised that he was bound by the court's verdict until such time as an appeal could be made, he "maintains absolutely his innocence" of the offence. "He had no hand, act or part in the outrage which occurred at Omagh."
Mr O'Higgins said his client was not a planner of the bomb, had not put the bomb together and had not been involved in moving it.
A second charge against Murphy of membership of an illegal organisation was adjourned until a future date.