Wadham was the second and eldest surviving child of Sir William Petre, a civil and canon lawyer serving King Henry VIII, and his wife, Gertrude, daughter of Sir John Tyrrell. Her portrait in Wadham College gives her age as sixty in 1595. When Wadham's mother died on May 28, 1541, she was brought up by Petre's second wife, Anne, who was also a Tyrrell by her first marriage. Later in life her writing skill and knowledge of Latin was evident and it is likely she was educated at her home, Ingatestone Hall, Essex. On September 3, 1555 she married Nicholas Wadham at St Botolph, Aldersgate, London.
The couple lived at Nicholas's family home in Merrifield, near Ilton, Somerset and produced no children. Nicholas died on October 20, 1609, and between 1612–13 Wadham had her armoury confiscated and was suspected of recusancy. In 1615 she was granted a formal pardon under the 1593 act against Popish recusants.
Dorothy was the sole executor of Nicholas's will, which stated the money was "for such uses and purposes" he had "requested her and she hath assented to". His wishes included founding a college in Oxford, which she did, noting "it would greatly offend my conscience to violate any jot of my husband's will". On his deathbed, Nicholas had summoned Sir John Davis to discuss his plans with Dorothy and their two men of business. Nicholas was persuaded by Davis to sign an instrument naming him jointly responsible with Dorothy for pursuing his plans for a college. Davis had been convicted as a traitor because of his part in the Essex conspiracy, and a recusant. His inclusion in the designs put the plan in jeopardy, in 1610 it was shown in parliament that he still refused the Church of England sacraments and may have wanted Wadham's foundation to be governed by his former college, Gloucester Hall. Dorothy wrote to the Lord High Treasurer, Robert Cecil a month after Nicholas's death, denying Davis's accusation that she did not intend to proceed with Nicholas's plans. An offer was made to Gloucester Hall, which was refused by the principal unless he was made head of the new foundation. Nicholas had intended an offer be made to Jesus College, but no evidence of such exists.
A site was acquired in February 1610 and the architect William Arnold was commissioned for its construction. A letter from King James I to Oxford City Council persuaded them to lower the asking price. Wadham managed to loosen Davis's ties with a collusive suit in chancery in July 1610, which established a trust excluding him. Her brother John Petre was key in raising the support at Westminster, but Wadham refused his offer of taking over the responsibility "which my dear husband so solely and absolutely trusted me with". On December 20, 1610 Wadham College received its royal letters patent, and statutes were drafted and approved by Wadham in 1612. The college was formally instituted in April 1613. The appointment of the warden, fellows, and scholars, and even on occasion the college cook, rested with Wadham, as outlined in a series of letters written by her man of business, John Arnold, and signed by her, as were the drafts of the statutes. Wadham never visited the college and relied in large on Arnold. Wadham died on May 16, 1618, at the Wadham dower house, Edge Barton Manor, in Branscombe, Devon, her body was taken to Merrifield and buried on June 16 with her husband in St Mary's Church, Ilminster.
- Davies, C. S. L. ‘Wadham, Dorothy (1534/5–1618)’, Oxford Dictionary of National Biography, Oxford University Press, 2004.