The Brimmon Oak in Newtown, Powys, won the title following a public vote.
Judges picked it as the overall champion of the four UK winners.
Beccy Speight, Woodland Trust chief executive, said: "Trees are inspirational in so many ways and our four winners clearly demonstrate how we cherish these natural landmarks."
Each winning tree will get a care grant of Â£1,000 and will go forward into the European Tree of the Year competition in February.
The Brimmon Oak, which has a girth of more than 6m (19.6ft), faced being destroyed by plans for the new Â£56m Newtown bypass as campaigners feared the close proximity would damage the roots.
Thousands of people signed a petition and the Welsh Government agreed to adjust the route to accommodate the oak with "minimal work" within a 15m (49ft) protected zone around the roots.
Ms Speight said trees "punctuate our lives and landscapes and tie us to our past, the equivalent of our best buildings but yet are far less protected".
Videos of each of the trees can be seen here.
A 500-year-old oak that a planned bypass road will be built around to prevent it being destroyed has been named as the UK's Tree of the Year.