It is the first time three parishes have represented the Bailiwick at the awards.
After winning three golds in the past, St Peter's was entered in the Champion of Champions.
However, they were unable to beat Ahoghill in Ulster, which won the class.
St Peter's Floral group member Corrina Walker said they were pleased with their gold award.
'Being a finalist in Champion of Champions category, as one of the top six communities in the UK, has been a unique opportunity for us,' she said.
'Winning a gold award is a tremendous result for our whole community. Everyone pulled out the stops to show that our tiny parish really is the best, with stunning seasonal displays outside businesses and homes, helping at our working parties and by supporting our fundraising events.
'Our thanks to everyone who has helped to achieve this remarkable success. We've all thoroughly enjoyed working together to make the parish an even lovelier place to work, live or visit.'
St Peter Port won a gold medal in the category for a coastal community with over 12,000 people. The class was won by Southport.
