Cllr Scully opposed the FG nominee Cllr Maria Byrne and defeated her nine votes to eight with the support of independents and Fianna Fáil.
The party’s national executive has completed a high-priority investigation into the affair.
The party leader on the council, Cllr Ger Fahy, has been informed the outcome will be announced today.
The five Fine Gael councillors were called before the national executive last Wednesday to give their individual versions of what happened at a party meeting prior to the election on June 27.
Fine Gael had a pact with Labour to rotate the mayoralty and this was to be Labour’s year.
However, Labour told Fine Gael it would support their nominee as they could not agree on a candidate.
Fine Gael met on the day of the mayoral election, but disagreement on how they should select a nominee emerged when four of the five members put their names forward.
Full-time FG officer Jim McMahon was called in to sort the matter out.
A PR vote was agreed and Cllr Maria Byrne won.
Some FG members claim Cllr Scully, when he did not win, left the meeting.
Cllr Scully, who was being groomed as a likely Dáil successor to Michael Noonan, said he was glad to get the opportunity to give his side of the story to the National Executive. The National Executive may decide to remove the party whip from Cllr Scully or it could expel him from the party.
If he is thrown out of the party it could deny Fine Gael and Labour sharing the office of mayor over the three final mayoralties, which will be bestowed by the present council.