Donal Ó Coisdealbha from Killester, north Dublin was arrested on explosive charges in the run-up to the visit of Prince Charles to Ireland in 2015.
Ó Coisdealbha admitted to the Dublin's Special Criminal Court that he was a dissident republican.
He was arrested during a Garda operation when explosive devices, improvised rockets, detonators, timing units and Semtex were discovered.
It was six days before the visit of Prince Charles and the Duchess of Cornwall to the west of Ireland in May 2015.
O'Coisdealbha had been under audio and visual surveillance for five months and was seen meeting convicted republicans in a pub near Dublin airport and in the city centre. He was also seen acting suspiciously at the back of Glasnevin Cemetery in north Dublin.
Gardaí (Irish police) believe an attack had been planned to coincide with the royal visit.
A 25-year-old dissident republican has been jailed in Dublin for five years.