Parliament Oak, which is believed to be 1,200-years-old and hosted a king's counsel under its boughs in the 13th century, had been in decline because of fly-tipping around it.
But the rescue project, funded by Nottinghamshire County Council's Building Better Communities initiative and Sherwood Forest Trust, has helped restore it to health.
Conservation officers from both organisations worked with local landowners to improve the area around Parliament Oak by removing illegally dumped waste.
They also created a timber post and rail fencing around the oak, located on the edge of Clipstone Forest between Edwinstowe and Mansfield, to prevent fly-tipping.
Saplings and scrub were cleared around the tree to allow more sunlight to reach it and locally sourced oak wood from the Thoresby Estate was used to provide a mulch for the soil.
Two parking spaces were created near the tree to allow for safe parking off the busy A6075.
New native hedgerows of hawthorn, blackthorn, hazel and holly will be planted to form a woodland edge around the parking bays and against the field boundary.
Nottinghamshire County councillor John Allin said: "This project is a great example of what can be achieved with partnership work and I hope that people will visit the site, respect it and look after it."