Parliament Oak is on the A6075 between Mansfield Woodhouse and Edwinstowe, in Nottinghamshire. It acted as a boundary marker, marking the northern entrance for a royal deer park. Sherwood Forest was important to the Royals, used for hunting deer and wild boar. This was popular with the Plantagenet Kings, with them staying nearby in the Kings Houses hunting lodge at clipstone, now known as King Johns Palace. The deer park survived into the 1800s.

The popular story of Parliament Oak is told about King John, who held Parliament under the tree in 1212. While out hunting with his nobles, a messenger brought the King news of a Welsh revolt and an insurrection in the north of England. Infuriated, he called Parliament there and then in order to gain consent to execute twenty eight Welsh hostages. The hostages were all boys aged between twelve and fourteen, being held at Nottingham Castle.

Another story states that the tree commemorates the Parliament held at the Kings Houses by Edward I, in 1290 while traveling to Scotland. The parliament opened on St. Michael's Day, lasting for two days, and some informal meets held under the trees branches. Many of the nobles who attended, lodged with important locals, clerks and others were lodged at nearby Warsop.

It is though by some historians, that the tree was planted at the time to commemorate the parliament. The oak was estimated to be about 400 years old in 1212. In 1790, Major Hayman Rooke described the oak 'Undoubtedly of very great antiquity' recording the size as slightly less than the Major Oak as it is today. The Parliament Oak today is a shadow of its former self. 300 years ago, the centre became hollow, eventually splitting into two. Both these sections continue to grow.