Deputy Prime Minister Eamon Gilmore issued an apology to the officers' families, saying he was "appalled and saddened" by the collusion finding.
"For years we have sought to get to the truth about their deaths," Gilmore said in a statement. "On behalf of the government and the people of Ireland, I apologize without reservation to the Breen and Buchanan families for any failings identified in the report on the part of the state or any of its agencies."
Irish Justice Minister Alan Shatter also apologized and described the murders as "two stark examples of the brutality which pervaded this island for many dark years."
Breen and Buchanan were the two highest-ranking Northern Ireland police officers to be murdered by the IRA's dominant faction, the Provisionals, which killed nearly 300 police as part of the underground army's failed 1970-1997 campaign to force Northern Ireland out of the U.K.
The two officers, who were in civilian clothes, were on their way home after the meeting in Dundalk when a gang of IRA militants ambushed their car. Breen tried to surrender, but both were shot dead at close range.
Officers of the Garda Siochana, Ireland's national police force, have repeatedly been accused of sympathizing with Provisional IRA attackers and aiding their efforts to kill Northern Ireland police and British soldiers in the 1970s and 1980s. But Smithwick was the first judge to be empowered by the government to get to the truth of any specific allegations.