She counts as one of the Valiant Sixty, the group of early itinerant preachers whose mission was to spread the spiritual message of the founder of the Quakers, George Fox.
In 1652, as a Quaker "Publisher of Truth", Mary Fisher publicly rebuked the vicar of Selby church in an address to his congregation after worship.
In December 1653, accompanied by Elizabeth Williams, Fisher walked to Cambridge as part of a Quaker drive to proselytise the south of England.
By order of the Mayor, they were taken to the market cross under the pretext that they were vagabonds, stripped to the waist and became the first Quakers to be publicly flogged for their ministry.
There they met with fierce hostility from the Puritan population and the Deputy Governor of the colony, Richard Bellingham, as news of the ostensibly heretical views of the Quakers had preceded them.
On arrival, they were taken ashore, imprisoned, forced to undress in public, and their bodies intimately examined for signs of witchcraft, Ann Austin reporting that one of the female searchers was "a man in a womans [sic] apparel".
[9] The magistrates, having ordered the women's prison window to be boarded up so as to isolate them, refused Upsall's request, the intention being to starve them to death.
Fisher and Austin were deported back to Barbados on the Swallow after five weeks' imprisonment, having been unable to share their faith with anyone except Upsall, who became the first North American Puritan convert to Quakerism.
[11] There she persuaded Köprülü Mehmed Pasha, the Grand Vizier, to arrange an audience for her with the Sultan, describing herself as an ambassador of "The Most High God".