A court has ruled that Stone serve the rest of his sentence for the 1988 Milltown Cemetery attack.
Stone had served 12 years of a 30-year term for the three murders at Milltown and three other sectarian killings.
He had been released on licence as part of the Good Friday Agreement but was jailed again for trying to kill Sinn Fein leaders at Stormont in 2006.
Stone was jailed for 16 years for the attempted murders of Gerry Adams and Martin McGuinness and other offences including possessing explosives.
The convicted killer had claimed to have been engaged in an act of performance art when he went to Stormont on the day Ian Paisley and Mr McGuinness were due to be nominated as Northern Ireland's first and deputy first ministers.
He was armed with knives, an axe, garrotte and a flight bag containing explosive fireworks, flammable liquids, a butane gas canister and fuses.
Stone, who suffers from hereditary motor neuropathy, was overpowered after trying to ignite the bag and throw it into the main foyer.
In 1988, Stone launched a gun and grenade attack on the Belfast funeral of three IRA members shot dead by British special forces in Gibraltar.
Three mourners - Thomas McErlean, John Murray and Kevin Brady - were killed and more than 50 injured.
Stone was also convicted of the murders of three other Catholic men - Patrick Brady, Kevin McPolin and Dermot Hackett - between 1984 and 1987.
Monday's court decision means the 58-year-old may not even be considered for release until March 2018.
Speaking in the court, Lord Chief Justice Sir Declan Morgan said of the murders: "There are serious aggravating factors. The effects on victims will live with them forever.
"The learned trial judge recommended a minimum term of 30 years before he should be considered for release and I agree. The appropriate minimum term in this case should be 30 years."
Loyalist killer Michael Stone must serve at least another five years in jail.