Edward Walsh of the Long Island Bar on Dorset St Upper was fined €250 and ordered to pay €750 in legal costs after he pleaded guilty at Dublin District Court to breaking the smoking ban.
He was prosecuted by the HSE following an inspection of the pub on the night of October 30 last. Judge John O'Neill said the breach was minimal.
Environmental health officer Claire Wilde told the court she went to the Long Island Bar and saw a man with a cigarette in his hand which he lit and started smoking.
She said he watched him for a couple of minutes and the customer must have noticed her and he then went to the designated smoking area outside.
The defence counsel told the court that it had been raining and was extremely wet at the time.
He asked Judge O'Neill to note that Mr Walsh, who has run the pub for the past three years and has no previous convictions, had not been present at the time but accepts responsibility.
The HSE said legal fees were €1,500 but the judge said the breach was minimal and he would have to pay €750 towards the costs.