Little is known of Tunstall's early life, except that he spent two years as a kitchen boy in the household of Sir Thomas Holland, perhaps at Lynn, Norfolk.

[2] William Warham, Archbishop of Canterbury, made Tunstall his chancellor on 25 August 1511, and shortly afterward he appointed him rector of Harrow on the Hill.

In 1515, Tunstall was sent to Flanders with Sir Thomas More, a friend since his school days, which More mentions in a glowing tribute in the opening paragraph of Utopia.

Although he was often engaged in time-consuming negotiations with the Scots, he took part in other public business and attended parliament where, in 1539, he participated in the discussion on the Bill of Six Articles.

Unlike Bishop John Fisher and Sir Thomas More, Tunstall adopted a policy of passive obedience and acquiescence regarding many matters for which he likely held little support during the troubled years following the English Reformation.

However, he continued to discharge his public duties without interruption and hoped in vain that the Earl of Warwick might be convinced to reverse the anti-Catholic policy of the Duke of Somerset.

When the Protestant Elizabeth I ascended to the throne, Tunstall refused to take the Oath of Supremacy and would not participate in the consecration of the Anglican Matthew Parker as Archbishop of Canterbury.

[12] The Anglican historian Albert F. Pollard wrote:[13] Tunstall's long career of eighty-five years, for thirty-seven of which he was a bishop, is one of the most consistent and honourable in the sixteenth century.

The extent of the religious revolution under Edward VI caused him to reverse his views on the royal supremacy and he refused to change them again under Elizabeth.