John O’Neill also said children would go to hell while “preaching the Gospel” at Braehead Shopping Centre, near Glasgow.
O’Neill denied he had done anything wrong, claiming he was exercising his freedom of speech and freedom of religion.
The 42-year-old from Hamilton went on trial at Paisley Sheriff Court charged with breaking Section 38(1) of the Criminal Justice and Licensing (Scotland) Act 2010 by shouting while expressing his religious views on 22 December last year.
He spent the lunch hour during his trial preaching to members of the public outside the town’s Piazza Shopping Centre.
O’Neill represented himself during his trial and gave evidence in his own defence, but did not swear an oath to God to tell the truth and instead affirmed he would tell the truth.
And, when asked by procurator fiscal depute Frankie Morgan why he had not taken the oath, he said: “The Bible tells me not to swear on anything.”
And he told the prosecutor he had acted the way he did on the day in question because he believed he was entitled to do so.
He explained: “I believe I had a right to do so.
“I am called as an Evangelist and that’s what I do regardless.
“We have a right to freedom of speech and freedom or religion and that includes manifesting it.”
Mr Morgan then asked why, just a few days before Christmas, in a shopping centre full of young families, he took it upon himself to “tell them Santa is a lie”.
O’Neill replied: “I have a right to speak the truth.
“The Bible tells me to speak the truth to every creature.
“This is very serious business. Men don’t know when they will die.
“Santa is a lie.
“I know it caused upset, but that’s not why I did it.
“Preaching the Gospel upsets people. Should I therefore stop preaching the Gospel?”
And he denied claims he had said “all the children will go to hell”, saying: “I believe children will go to heaven.”
O’Neill then touched his Bible, which was sitting on the witness stand, as he said: “A man who doesn’t live by this said I said that.
“Jesus says ‘I am the way, the truth and the light’, I live by this.
“Why would I then say otherwise?”
And, when asked if he was deliberately telling lies to get himself out of trouble, he replied: “Not at all. I accept what comes my way.
“Men will kill you and think they’re doing God a favour.
“Even if they want my head on a plate, I forgive them. It is what it is.”
But Sheriff Lindsey Kooner rejected his claims that he had not broken the law by his actions and convicted him of the single charge against him, ruling it could cause a reasonable person to suffer fear or alarm.
She then deferred sentence for three months for O’Neill, who is part of a team of street evangelists who operate in Glasgow, to be of good behaviour.
He is due to return to the dock in June to learn his fate.