Tommy Sheridan was not at a festival in Glasgow organised by the Scottish Socialist Party on the day it is alleged he was at a swingers club in Manchester, a court has heard.
Ex-Scottish Socialist Party treasurer Allison Kane said Mr Sheridan did not attend the event on 27 September 2002.
A previous witness, Katrine Trolle, had told the court Mr Sheridan was in Cupid's club on that date.
Mr Sheridan and his wife Gail, both 46, are on trial for perjury.
The former MSP and his wife deny lying under oath during Mr Sheridan's successful defamation action against the News of the World in 2006.
Mr Sheridan won £200,000 in damages after the newspaper printed allegations about his private life, claiming he was an adulterer who had visited a swingers club.
Ms Kane told the High Court in Glasgow that she had organised the Scottish Socialist Party's People's Festival in venues across Glasgow to raise money for the party and showcase the cultural side of the SSP.
She said she expected Mr Sheridan to attend because he was "one of my staunchest supporters within the party".
She told Advocate Depute Alex Prentice QC: "He wasn't at the Friday night event, neither was he at the Saturday (event) during the day, but he was at Saturday evening and the Monday. I remember that because it was my birthday."
The politician has previously shown the trial his diary for that year, with the words: "SSP People's Festival. Friday - Monday. Must attend" written in the space for 27 September.
Earlier the trial heard that the former SSP leader would have been forced out if he had not resigned when allegations were made against him in 2004.
The court was told the statement was contained in an affidavit given by former SSP policy convener Alan McCombes to the Sunday Herald.
The document states the party would have "put information into the public domain" to force Mr Sheridan to resign if he had not offered to.
He said the party wanted Mr Sheridan to admit to the allegations contained in the News of the World or say nothing at all.
Mr McCombes later went to jail for refusing to hand over minutes of the SSP meeting on 9 November 2004, at which it is alleged that Mr Sheridan admitted to sex allegations.
Defending himself, Mr Sheridan asked Ms Kane if Mr McCombes's actions had not been cynical in the extreme.
He said that on the one hand Mr McCombes went "scurrying to the bourgeois press" while on the other going to jail to keep the minutes secret.
Ms Kane said that Mr Sheridan had "scurried to the papers" and "spun a web of lies off the bat" and asked if that was not cynical.
It is alleged that Mr Sheridan made false statements as a witness in his defamation action against the News of the World on 21 July 2006.
He also denies another charge of attempting to persuade a witness to commit perjury shortly before the 23-day legal action got under way.
Mrs Sheridan denies making false statements on 31 July 2006, after being sworn in as a witness in the civil jury trial at the Court of Session in Edinburgh.