The priory was founded in 1142 as the Augustinian priory of Clack, and dedicated to Saint Mary.
It was well-sited on a high ridge near a holy well, with further springs nearby; there is some evidence that a chapel of the era of Henry I already existed at the holy well.

The founder, Walter FitzEdward de Salisbury, was the son of Edward de Salisbury, a High Sheriff of Wiltshire; he gave lands for a priory as a daughter house of St. Mary's Abbey, Cirencester, according to its charter, "to serve God forever!".
After the death of his wife, he "took the tonsure and habit of the canons" and on his death in 1147, was buried in the Priory, near the choir.
His descendants, the Earls of Salisbury remained closely connected with the priory for many years.
In 1190 thirteen of the canons migrated to form the first community of Cartmel Priory, now in Cumbria, which had been recently founded by William Marshal, Earl of Pembroke.

Throughout most of its early history, the priory also enjoyed royal support, being granted a charter by Henry II some time between 1173 and 1179; Richard I also lent assistance for the priory to break away from the abbot of Cirencester to become a priory in its own right, and King John, a frequent visitor, intervened to confirm this secession.
This tradition continued with the grant of royal protection by Henry III, who visited in 1235.

By the 14th century, Bradenstoke Priory had gained wealth and lands in nine counties besides Wiltshire.
This does not imply that the community lived in luxury or were corrupt.
It was not a backwater, since in its latter years it had benefitted from the residence of its then prior, Thomas Wallashe, in the household of Cardinal Bainbridge, Archbishop of York, during his embassy in Rome (1509–1514), leading to grant of extensive papal privileges to the priory.
The priory was founded in 1142 as the Augustinian priory of Clack, and dedicated to Saint Mary. It was well-sited on a high ridge near a holy well, with further springs nearby; there is some evidence that a chapel of the era of Henry I already existed at the holy well.
The founder, Walter FitzEdward de Salisbury, was the son of Edward de Salisbury, a High Sheriff of Wiltshire; he gave lands for a priory as a daughter house of St. Mary's Abbey, Cirencester, according to its charter, "to serve God forever!". After the death of his wife, he "took the tonsure and habit of the canons" and on his death in 1147, was buried in the Priory, near the choir. His descendants, the Earls of Salisbury remained closely connected with the priory for many years. In 1190 thirteen of the canons migrated to form the first community of Cartmel Priory, now in Cumbria, which had been recently founded by William Marshal, Earl of Pembroke.
Throughout most of its early history, the priory also enjoyed royal support, being granted a charter by Henry II some time between 1173 and 1179; Richard I also lent assistance for the priory to break away from the abbot of Cirencester to become a priory in its own right, and King John, a frequent visitor, intervened to confirm this secession. This tradition continued with the grant of royal protection by Henry III, who visited in 1235.
By the 14th century, Bradenstoke Priory had gained wealth and lands in nine counties besides Wiltshire. This does not imply that the community lived in luxury or were corrupt. It was not a backwater, since in its latter years it had benefitted from the residence of its then prior, Thomas Wallashe, in the household of Cardinal Bainbridge, Archbishop of York, during his embassy in Rome (1509–1514), leading to grant of extensive papal privileges to the priory.
Bradenstoke Priory