Aaron Wallace, 28, and Christopher Francis Kerr, 30, are serving life sentences for their roles in the sectarian killing of 15-year-old Michael McIlveen in Ballymena, Co Antrim 11 years ago.
Their lawyers argued that a revised law on joint enterprise cases rendered their convictions unsafe.
But the Court of Appeal ruled both defendants were part of a gang of Protestant youths who chased the victim, knowing that another in their group, Mervyn Moon, was armed with a dangerous weapon which could cause grave harm.
Rejecting their case, Lord Chief Justice Sir Declan Morgan said: “In our view the inference that each appellant participated in a joint attack upon the deceased, intending that Moon could use the baseball bat to inflict serious bodily injury in that attack, is overwhelming.”
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Michael McIlveen was struck on the head after being pursued into an alleyway in his home town in May 2006.
The teenager, known to his friends and family as Mickybo, died later from brain injuries inflicted during the assault.
The man who wielded the bat, 29-year-old Moon, from Douglas Terrace in the town, was jailed for a minimum 10 years.
In 2009 Kerr, of Carnduff Drive, and Wallace, from Moat Road, both in Ballymena, were also found guilty of the schoolboy’s murder.
Although those convictions were quashed the pair entered guilty pleas as their retrial was due to get under way four years ago.
Admissions were made on the basis of a statement of facts agreed by prosecution and defence lawyers in relation to the roles they played in events surrounding Michael’s death.
Wallace was ordered to serve at least eight years behind bars, while Kerr’s tariff was set at a year higher because he had obtained the baseball bat.
Both men’s legal teams contended that a Supreme Court ruling on the interpretation of joint enterprise casts doubt on the safety of their convictions.
The new law includes a requirement that to be found guilty a secondary party must share an intention to inflict serious harm on the victim – foresight alone is not enough.
The Court of Appeal heard Michael was knocked to the ground by the blow from Moon.
Wallace and Kerr were said to be part of a group who also kicked the victim during the assault.
It was claimed that neither of them had foresight of any grievous harm.
However, Sir Declan, who heard the appeal with Lord Justice Weir and Mr Justice Deeny, found that both participated in the chase and knew Moon was armed with the bat when they followed him to the scene of the fatal attack.
“This was an offensive rather than a defensive action,” he said.
“The pursuit of the deceased up the alleyway could only have been for the same purpose as the initial chase, that is to assault the deceased.”
Declaring both convictions safe, the Lord Chief Justice confirmed: “Leave to appeal is refused in each case.”