They travelled to London with a Semtex high-explosive bomb and six incendiary devices but were arrested after a surveillance operation by police and the security service, MI5.
Sentencing them, Mr Justice Klevan said: "Your arrogance and callousness to those who would have suffered at your hands is breathtaking."
The ringleader, Anthony Hyland, 26, who was in the fourth year of an arts degree at University College, Dublin, was jailed for 25 years. Liam Grogan, 22, who had just completed a commerce degree at the same university, and Darren Mulholland, 20, who was studying theoretical physics at Queen's University, Belfast, were sentenced to 22 years.
They had denied that, with others unnamed, they conspired to cause explosions between June 1 and July 11 last year. The three showed no emotion as they were convicted by the jury after nearly 13 hours of deliberations. When sentenced Hyland said: "That's no problem."
The students were monitored from the moment Hyland arrived at Stansted airport last July. Although they stayed at separate locations and practised anti-surveillance techniques, they were tracked and filmed meeting in London parks and at furniture shops.
Hyland was seen visiting the reference section of a public library where he consulted a House of Commons reference book - leaving his fingerprints in the section for MPs whose names start with the letter `s'. When he was arrested on July 10, he had a rucksack containing the six incendiary bombs.
Mr Justice Klevan said that although the trio may not have had the intention of taking life, "there was a substantial risk of death and injury".
He said: "Thankfully, in consequence of the vigilance of the police, you were caught before your bombs could wreak havoc. If the incendiary devices had been placed in shops and ignited, the damage would have been enormous. If the Semtex bomb had been placed and exploded, the result would have been horrifying."
As part of the police investigation, an undercover woman officer successfully applied to rent a room in the north London flat where Hyland was staying. Inside, police found another of the student's rucksacks, containing a timer, a detonator and 2lb of Semtex.
Nigel Sweeney, for the prosecution, told the court that Hyland had brought the bombing devices from Ireland in plastic food storage boxes. They had been wrapped in plastic film and covered in talcum powder to deceive sniffer dogs.
Although he declined to answer questions during 12 interviews, when charged Hyland said: "I would like to state emphatically there was never any intention to endanger life."
This was an admission he had intended to cause injury to property, said Mr Sweeney.Reuse content