Around 6,000 coins and a large number of rings, necklaces and chains were in a wooden box near the town of Freistadt, 85 miles northwest of the capital, Vienna, and near the border with the Czech Republic.
The treasure is thought to date from the 13th century and includes gold and silver coins said to be in "excellent condition".
Several coins were minted in England, others in Jerusalem and some in Bohemia, now the North-west part of the Czech Republic. Gold metal sheets and tools in the box have led archaeologists to speculate that the collection belonged to a goldsmith.
The hoard was discovered purely by chance. The farmer is believed to have brought his tractor to a halt after his plough got caught on the box. Although he had little idea of what the box contained - or its value - he contacted the police and the local museum.
It has proved to be a profitable day's work. The farmer and a worker who was with him have been rewarded with 500,000 Austrian schillings (pounds 25,000) apiece from the Schloss Museum in the nearby city of Linz.
The museum described the find as "the largest ensemble of late medieval jewellery ever found in Europe."
But officials refused to place a price on the value of the collection.
The discovery was made almost a year ago but was only now disclosed by the Schloss museum, amid security fears that the collection might be targeted by professional thieves.
Neither the farmer's name nor the exact location of the find has been made public, in an effort to discourage prospectors flooding to the area in the hope of unearthing further booty.
The museum has identified, dated and cleaned the coins, repairing many of them. They are expected to go on display at the museum in December.Reuse content