Silvano Orsi had fought to bring the case to court for five years
The brother of the UAE president has been found guilty in a Swiss court of beating a US citizen with a belt at a hotel bar in Geneva in 2003.
The tribunal fined Sheikh Falah al-Nahyan 10,000 Swiss francs (£4,930, $9,820). In addition he received a suspended penalty of 540,000 francs.
The judgement said that the sheikh repeatedly hit Silvano Orsi with a steel-buckled belt.
Sheikh Nahyan, who maintains his innocence, is expected to appeal.
The court said the sheikh inflicted "bodily harm with the use of a dangerous object" on Mr Orsi, a resident of Rochester, New York, after Mr Orsi declined an offer of a bottle of champagne from the sheikh.
The sheikh also has to pay costs for the lawyers and the proceedings amounting to 2,879 Swiss francs (US $2,829), the court ruled.
Mr Orsi, who had sought damages for injuries, said he was happy with the judgement.