The four surviving original copies of Magna Carta will be brought together in 2015 for the first time in history, the British Library has announced.
The event will take place over three days and launch a year of celebrations across the UK and the world to mark the document's 800th anniversary.
Magna Carta, meaning Great Charter, was agreed at Runnymede, Surrey in 1215.
The document is seen as the cornerstone of Britain's constitution, outlining a set of basic rights.
There are four surviving copies of Magna Carta - two copies belong to the British Library, one copy is owned by Lincoln Cathedral and one by Salisbury Cathedral.
All three organisations will be involved in the event, which will be held at the British Library in London.
The library said it would be a "once-in-a-lifetime opportunity for researchers and the public to see the documents side-by-side".
The manuscripts will be examined by some of the world's leading experts.
The library said the unification of the documents would allow them to be studied much more closely, particularly faded or obscured parts of the text.
Historians would also be able to look for new clues about the identity of the writers of the texts, which is still unknown.
The charter was issued by King John as a way solving the political crisis he faced when powerful barons rebelled against him and captured London.
Although almost all the clauses have been repealed in modern times, the document established a number of important principles that have been copied around the world.
These include the principle that no-one is above the law - including the king - the right to a fair trial, and limits on taxation without representation.
It inspired the US Constitution and the Universal Declaration of Human Rights.
Claire Breay, lead curator of medieval and earlier manuscripts at the British Library, said: "Magna Carta is the most popular item in the library's treasures gallery, and is venerated around the world as marking the starting point for government under the law."
The Dean of Salisbury, the Very Reverend June Osborne, praised the values of social justice in Magna Carta and said she hoped the unification would increase awareness of the charter "to a huge new audience".
The Very Reverend Philip Buckler, Dean of Lincoln, said bringing together all four copies would be of "national significance" and would mark a "pivotal point" in the anniversary year.
Lincoln Cathedral will be opening a new purpose-built Magna Carta centre in Lincoln Castle during the anniversary year.