Cathal McLaughlin, 60, grabbed hold of the waitress and touched her ”hinder parts” as she served him and his friends drinks at the city’s Three Sisters pub last year.
McLaughlin denied assaulting the woman and claimed he had pulled her closer to him in a bid to hear what she was saying due to him being partially deaf.
But CCTV showed the veteran republican sexually assaulting the staff member, who cannot be identified due to legal reasons, by touching her up during his drunken night out.
McLaughlin, from Cloughmills, Northern Ireland, denied the charge against him but was found guilty of the attack when he stood trial at Edinburgh Sheriff Court earlier this month.
Sheriff Donald Corke placed the shamed councillor on the Sex Offenderss Register on an interim basis and sentence was deferred to next month for social work reports.
McLaughlin has this week been expelled from the party where he represented the area of Ballymoney on Causeway Coast and Glens Borough Council.
In a statement, Sinn Fein said they have written to McLaughlin to inform him of his expulsion from the party following the conviction. It is not known if McLaughlin informed council chiefs that had stood trial in Scotland.
A spokesperson said: “Sinn Fein has written to councillor Cathal McLaughlin upon receipt of information that he has been convicted in a Scottish court of a serious criminal offence.
“Our thoughts are with the victim of this serious crime of sexual assault.”
The spokesperson added that McLaughlin failed to notify the party that he was subject to ‘criminal proceedings’.
They said: “Given the severity of the offence, his membership of Sinn Féin is terminated with immediate effect.”
A spokesperson for Causeway Coast and Glens Council said: “Causeway Coast and Glens Borough Council can confirm that Cathal McLaughlin resigned from his position on July 23rd 2022.”
McLaughlin was found guilty of sexually assaulting a woman by handling her hinder parts at the Three Sisters, Cowgate, Edinburgh, on October 15 last year.