The result is the best ever for a UK tree in the seven-year history of the continent-wide contest, organised by the Czech-based Environmental Partnership Association.
The ancient pollarded oak, near Newtown, Powys, is thought to be at least 500 years old, has been cared for by one family for generations. In 2015 it was threatened with destruction by a new bypass, but this was averted after a public campaign.
The contest gained some high-profile UK media coverage this year, including a five-minute spot last month on BBC Radio 2's flagship Chris Evans Breakfast Show.
The full results of the 2017 contest are:
• 1st: Oak Jósef, Poland – 17,597 votes
• 2nd: Brimmon Oak, Wales – 16,203 votes
• 3rd: The Lime Tree at Lipka, Czech Republic – 14,813 votes
• 5th: Sycamore Gap tree, England – 7,123 votes
• 6th: Holm Oak, Northern Ireland – 7,101 votes
• 8th: Ding Dong Tree, Scotland – 6,327 votes
The award was made by European Commissioner for Environment Karmenu Vella at the European Parliament in Brussels yesterday to coincide with the International Day of Forests.
Woodland Trust chief executive Beccy Speight said: "The UK is rightly renowned for having some of the best examples of ancient trees in Europe, so it's good to see them finally achieving recognition in the competition."
The UK entries in the contest have benefitted from a care grant from the People's Postcode Lottery, which will pay for arboricultural assessments, interpretation or even a celebratory event.