She was born on 1 September 1739 (O.S.) in Leytonstone. Meeting with opposition from her well-to-do family and its lifestyle, because of her religious inclinations she left home in 1760, taking lodgings in London. She joined the London society and became involved in the great Methodist revival there in 1761-62. In 1762 she went to live in her own house in Leytonstone where, with Sarah Crosby and Sarah Ryan, she established a Christian community caring for needy children and began 'to exhort, and to read and expound the scriptures'. In June 1768, partly for financial reasons, the community moved to Cross Hall, Morley, a farm left to her by her parents near Leeds. Mary corresponded with John Wesley, consulting him about her call to preach. Although preaching by women was not then permitted among the Methodists, he admitted that she had an 'extra-ordinary call', but stopped short of agreeing to her becoming an itinerant preacher.
Turning down an offer of marriage from a wealthy businessman, on 12 November 1781 she married John Fletcher of Madeley, whom she had known for a quarter of a century, at Batley parish church and they exercised what was effectively a joint ministry. To avoid giving local offence, Mary 'spoke' regularly in the Madeley tithe barn. After her husband's death in 1785, she continued her work in Madeley until a few weeks before her own death, acting as an unofficial curate to his successor. Wesley was unsuccessful in trying to persuade her to leave Madeley for London. She died on 9 December 1815 and was buried with her husband in Madeley churchyard.
' My dear Sister,
'Yours , I believe, is one of the few marriages that are made in heaven. Better late than never. My friend had thoughts of proposing to you (I am his witness) 20 years ago: but he bore false witness against himself so that he then sought not you but yours. I sincerely rejoice that he has at last found out his twin-soul, and trust you will be happier by your meeting thro' all eternity
'My friend's longer or shorter continuance here will depend chiefly on his advisableness. He is (I know & he knows) a mule by nature: but is become by grace, and by the wisdom from above, easy to be entreated. Be a litle child yourself, & he will be led by you into all that is right. As to the measure of his labours, we will allow him a vote, & private judgment: but then the last resource must be with you. You have a negative. And while he hearkens to the voice of his wife, he will live and prosper.'
Charles Wesley to Mrs, Mary Fletcher, March 13th 1782 (original at Emory University)
'Now my breath is very short, and many complaints render me unable to travel; I therefore feel the Lord leads me to apply to what little I can do in my own preaching room, where the congregation increases, and many come from far, and I am, through mercy, at present carried through six or seven meetings, in a week, of different sorts. For some years I was often led to speak from a text, of late I feel greater approbation in what we call expounding, taking a part or whole of a chapter, and speaking on it. We have lately found the Lord very present, and many souls have been blest I do look on the call of women as an extra - not an ordinary call; therefore I strove, and do strive now so to act, not out of custom, but only when I have a clear leading thereto, and this leading may and will differ at different parts of our lives, but to follow the cloud is the thing I aim at, and the soul feels a peace and comfort in so doing, for "where the spirit of the Lord is there is liberty." '
Mary Fletcher to Mrs. Taft, 28 November 1803, quoted in L.F. Church, More about the Early Methodist People (1949) pp.146-7