Sinn Fein suffered a setback in the Northern Ireland Assembly on Monday night when if failed to block new legislation barring those with a serious conviction from working as special political advisers.
Although only one party member will be affected by the new rule, Sinn Fein protested that the new rule goes against one of the central features of the peace process, which allows ex-prisoners to take part in politics.
But it failed to attract support from other parties, so that the ban was passed by 56 votes to 28.
The result is seen as a personal victory for Ann Travers, a Belfast woman who has waged an emotional two-year campaign in the wake of the IRA murder of her sister in a 1984 attack in which her father, a magistrate, was seriously injured.
The immediate effect will be to disqualify former IRA member Paul Kavanagh from his job as special adviser to Sinn Fein's Martin McGuinness, who is deputy first minister in the Assembly.
Mr Kavanagh served more than a decade in British prisons after being convicted of three murders in IRA bombings in London. He is married to Sinn Fein MEP Martina Anderson, who was also jailed for IRA activity in Britain.
Ms Travers's campaign began when Sinn Fein appointed as a special adviser Mary McArdle, who had served a life sentence for the murder of her sister. She was later quietly moved from the position but Ms Travers persisted in arguing that those convicted of killings and other serious offences should not be given jobs with salaries paid from the public purse.
Her campaign succeeded in pressurising a moderate nationalist party to change its position and drop its initial opposition to the legislation.
Ms Travers said after the vote: “I'm so pleased. Everything I've done, I've done out of love for my sister Mary who was beautiful, gifted, talented, and didn't deserve to die the way that she did.
“She certainly didn't deserve to have her memory stamped on.”
The new legislation will affect special advisers who have received sentences of more than five years in prison. There is to be an appeals process during which victims can have a say.
Representatives of a number of victims groups were at the Belfast Assembly for the lengthy debate on the issue.
The new rules will not affect several dozen Sinn Fein members who work at Stormont and have previously served sentences for IRA offences. These include a number of ministers and ex-ministers, including Mr McGuinness.
Others include Assembly members and party staff, including a number who were given life sentences for murder.