Marshall was elected Dean (head) of Christ Church, Oxford in 1553, a post he held until 1559.
[3][4] He is thought to have been the son of William Marshall, was said to be from Kent, and was a scholar of Corpus Christi College, Oxford, from 1532 until 1538.
[5] At Corpus Marshall was Greek lecturer, and noted as a strong Roman Catholic traditionalist.
In Edward VI's reign he is said to have turned Protestant, and was vice-chancellor in 1552, but he changed his views under Mary I.
In 1554 he took part in the Oxford disputation on transubstantiation, was one of the witnesses against Thomas Cranmer, aided in the degradation of Nicholas Ridley.
He found refuge with Henry Clifford, 2nd Earl of Cumberland and Christopher Metcalf in the north.