John Wesley was born in 1703 in Epworth, 23 miles (37 km) north-west of Lincoln, as the fifteenth child of Samuel Wesley and his wife Susanna Wesley (née Annesley). Samuel Wesley was a graduate of the University of Oxford and a poet who, from 1696, was rector of Epworth. He married Susanna, the twenty-fifth child of Samuel Annesley, a dissenting minister, in 1689. Ultimately, she bore nineteen children, of which nine lived beyond infancy. She and Samuel Wesley had become members of the Church of England as young adults.

During Wesley's absence, his younger brother Charles (1707–88) matriculated at Christ Church. Along with two fellow students, he formed a small club for the purpose of study and the pursuit of a devout Christian life. On Wesley's return, he became the leader of the group which increased somewhat in number and greatly in commitment. The group met daily from six until nine for prayer, psalms, and reading of the Greek New Testament. They prayed every waking hour for several minutes and each day for a special virtue. While the church's prescribed attendance was only three times a year, they took Communion every Sunday. They fasted on Wednesdays and Fridays until three o'clock as was commonly observed in the ancient church. In 1730, the group began the practice of visiting prisoners in jail. They preached, educated, and relieved jailed debtors whenever possible, and cared for the sick.

Apart from his disciplined upbringing, a rectory fire which occurred on 9 February 1709, when Wesley was five years old, left an indelible impression. Some time after 11:00 pm, the rectory roof caught on fire. Sparks falling on the children's beds and cries of "fire" from the street roused the Wesleys who managed to shepherd all their children out of the house except for John who was left stranded on an upper floor. With stairs aflame and the roof about to collapse, Wesley was lifted out of a window by a parishioner standing on another man's shoulders. Wesley later used the phrase, "a brand plucked out of the fire", quoting Zechariah 3:2, to describe the incident. This childhood deliverance subsequently became part of the Wesley legend, attesting to his special destiny and extraordinary work.

As in many families at the time, Wesley's parents gave their children their early education. Each child, including the girls, was taught to read as soon as they could walk and talk. They were expected to become proficient in Latin and Greek and to have learned major portions of the New Testament by heart. Susanna Wesley examined each child before the midday meal and before evening prayers. Children were not allowed to eat between meals and were interviewed singularly by their mother one evening each week for the purpose of intensive spiritual instruction. In 1714, at age 11, Wesley was sent to the Charterhouse School in London (under the mastership of John King from 1715), where he lived the studious, methodical and, for a while, religious life in which he had been trained at home.

As his societies needed houses to worship in, Wesley began to provide chapels, first in Bristol at the New Room, then in London (first The Foundery and then Wesley's Chapel) and elsewhere. The Foundery was an early chapel used by Wesley. The location of the Foundery is shown on an 18th-century map, where it rests between Tabernacle Street and Worship Street in the Moorfields area of London. When the Wesleys spotted the building atop Windmill Hill, north of Finsbury Fields, the structure which previously cast brass guns and mortars for the Royal Ordnance had been sitting vacant for 23 years; it had been abandoned because of an explosion on 10 May 1716.

In June 1720, Wesley entered Christ Church, Oxford. In 1724, he graduated as a Bachelor of Arts and decided to pursue a Master of Arts degree. He was ordained a deacon on 25 September 1725, holy orders being a necessary step toward becoming a fellow and tutor at the university.

In March 1726, Wesley was unanimously elected a fellow of Lincoln College, Oxford. This carried with it the right to a room at the college and regular salary. While continuing his studies, he taught Greek, lectured on the New Testament and moderated daily disputations at the university. However, a call to ministry intruded upon his academic career. In August 1727, after taking his master's degree, Wesley returned to Epworth. His father had requested his assistance in serving the neighbouring cure of Wroot. Ordained a priest on 22 September 1728, Wesley served as a parish curate for two years. He returned to Oxford in November 1729 at the request of the Rector of Lincoln College and to maintain his status as junior fellow.

For all of his outward piety, Wesley sought to cultivate his inner holiness or at least his sincerity as evidence of being a true Christian. A list of "General Questions" which he developed in 1730 evolved into an elaborate grid by 1734 in which he recorded his daily activities hour-by-hour, resolutions he had broken or kept, and ranked his hourly "temper of devotion" on a scale of 1 to 9. Wesley also regarded the contempt with which he and his group were held to be a mark of a true Christian. As he put it in a letter to his father, "Till he be thus contemned, no man is in a state of salvation."

John Wesley had strong links with the North West of England, visiting Manchester on at least fifteen occasions between 1733 and 1790. In 1733 and 1738 he preached at St Ann's Church and Salford Chapel, meeting with his friend John Clayton. In 1781 Wesley opened the Chapel on Oldham Street part of the Manchester and Salford Wesleyan Methodist Mission, now the site of Manchester's Methodist Central Hall.

On 14 October 1735, Wesley and his brother Charles sailed on The Simmonds from Gravesend in Kent for Savannah in the Province of Georgia in the American colonies at the request of James Oglethorpe, who had founded the colony in 1733 on behalf of the Trustees for the Establishment of the Colony of Georgia in America. Oglethorpe wanted Wesley to be the minister of the newly formed Savannah parish, a new town laid out in accordance with the famous Oglethorpe Plan.

Wesley arrived in the colony in February 1736. He approached the Georgia mission as a High churchman, seeing it as an opportunity to revive "primitive Christianity" in a primitive environment. Although his primary goal was to evangelize the Native Americans, a shortage of clergy in the colony largely limited his ministry to European settlers in Savannah. While his ministry has often been judged to have been a failure in comparison to his later success as a leader in the Evangelical Revival, Wesley gathered around him a group of devoted Christians who met in a number of small group religious societies. At the same time, attendance at church services and Communion increased over the course of nearly two years in which he served as Savannah's parish priest.

Nonetheless, Wesley's High Church ministry was controversial among the colonists and it ended in disappointment after Wesley fell in love with a young woman named Sophia Hopkey. He hesitated to marry her because he felt that his first priority in Georgia was to be a missionary to the Indigenous Americans, and he was interested in the practice of clerical celibacy within the early Christianity. Following her marriage to william Williamson, Wesley believed Sophia's former zeal for practising the Christian faith declined. In strictly applying the rubrics of the Book of Common Prayer, Wesley denied her Communion after she failed to signify to him in advance her intention of taking it. As a result, legal proceedings against him ensued in which a clear resolution seemed unlikely. In December 1737, Wesley fled the colony and returned to England.

Wesley allied himself with the Moravian society in Fetter Lane. In 1738 he went to Herrnhut, the Moravian headquarters in Germany, to study. On his return to England, Wesley drew up rules for the "bands" into which the Fetter Lane Society was divided and published a collection of hymns for them. He met frequently with this and other religious societies in London but did not preach often in 1738, because most of the parish churches were closed to him.

Whitefield inclined to Calvinism. In his first tour in America, he embraced the views of the New England School of Calvinism. When in 1739 Wesley preached a sermon on Freedom of Grace, attacking the Calvinistic understanding of predestination as blasphemous, as it represented "God as worse than the devil," Whitefield asked him not to repeat or publish the discourse, as he did not want a dispute. Wesley published his sermon anyway. Whitefield was one of many who responded. The two men separated their practice in 1741. Wesley wrote that those who held to unlimited atonement did not Desire separation, but "those who held 'particular redemption' would not hear of any accommodation."

In addition to his Sermons and Notes are his Journals (originally published in 20 parts, London, 1740–89; new ed. by N. Curnock containing notes from unpublished diaries, 6 vols., vols. i–ii, London and New York, 1909–11); The Doctrine of Original Sin (Bristol, 1757; in reply to Dr. John Taylor of Norwich); An Earnest Appeal to Men of Reason and Religion (originally published in three parts; 2nd ed., Bristol, 1743), an elaborate defence of Methodism, describing the evils of the times in society and the church; and a Plain Account of Christian Perfection (1766).

When the debt on a chapel became a burden, it was proposed that one in 12 members should collect offerings regularly from the 11 allotted to him. Out of this grew the Methodist class-meeting system in 1742. To keep the disorderly out of the societies, Wesley established a probationary system. He undertook to visit each society regularly in what became the quarterly visitation, or conference. As the number of societies increased, Wesley could not keep personal contact, so in 1743 he drew up a set of "General Rules" for the "United Societies". These were the nucleus of the Methodist Discipline, still the basis.

As the number of Preachers and preaching-places increased, doctrinal and administrative matters needed to be discussed; so John and Charles Wesley, along with four other clergy and four lay Preachers, met for consultation in London in 1744. This was the first Methodist conference; subsequently, the conference (with Wesley as its president) became the ruling body of the Methodist movement. Two years later, to help Preachers work more systematically and societies receive services more regularly, Wesley appointed "helpers" to definitive circuits. Each circuit included at least 30 appointments a month. Believing that the preacher's efficiency was promoted by his being changed from one circuit to another every year or two, Wesley established the "itinerancy" and insisted that his Preachers submit to its rules.

As the societies multiplied, they adopted the elements of an ecclesiastical system. The divide between Wesley and the Church of England widened. The question of division from the Church of England was urged by some of his Preachers and societies, but most strenuously opposed by his brother Charles. Wesley refused to leave the Church of England, believing that Anglicanism was "with all her blemishes, [...] nearer the Scriptural plans than any other in Europe". In 1745 Wesley wrote that he would make any concession which his conscience permitted, to live in peace with the clergy. He could not give up the doctrine of an inward and present salvation by faith itself; he would not stop preaching, nor dissolve the societies, nor end preaching by lay members. As a cleric of the established church he had no plans to go further.

When, in 1746, Wesley read Lord King's account of the primitive church, he became convinced that apostolic succession could be transmitted through not only bishops, but also Priests. He wrote that he was "a scriptural episkopos as much as many men in England." Although he believed in apostolic succession, he also once called the idea of uninterrupted succession a "fable".

Wesley's legacy is also preserved in Kingswood School, which he founded in 1748 to educate the children of the growing number of Methodist Preachers. Also, one of the four form houses at the St Marylebone Church of England School, London, is named after John Wesley.

In his Christian Library (1750), he writes about Mystics such as Macarius of Egypt, Ephrem the Syrian, Madame Guyon, François Fénelon, Ignatius of Loyola, John of Ávila, Francis de Sales, Blaise Pascal, and Antoinette Bourignon. The work reflects the influence of Christian mysticism in Wesley's ministry from the beginning to the end, although he ever rejected it after the failure in Georgia mission.

Wesley wrote, edited or abridged some 400 publications. As well as theology he wrote about music, marriage, Medicine, abolitionism and politics. Wesley was a logical thinker and expressed himself clearly, concisely and forcefully in writing. His written sermons are characterised by spiritual earnestness and simplicity. They are doctrinal but not dogmatic. His Forty-Four Sermons and the Notes on the New Testament (1755) are Methodist doctrinal standards. Wesley was a fluent, powerful and effective preacher; he usually preached spontaneously and briefly, though occasionally at great length.

He is described as below medium height, well proportioned, strong, with a bright eye, a clear complexion, and a saintly, intellectual face. Though Wesley favoured celibacy than marital bond, he married very unhappily at the age of 48 to a widow, Mary Vazeille, described as "a well-to-do widow and mother of four children." The couple had no children. Vazeille left him 15 years later. John Singleton writes: "By 1758 she had left him – unable to cope, it is said, with the competition for his time and devotion presented by the ever-burgeoning Methodist movement. Molly, as she was known, was to return and leave him again on several occasions before their final separation." Wesley wryly reported in his journal, "I did not forsake her, I did not dismiss her, I will not recall her."

Wesley also wrote on Divine physics, such as in Desideratum, subtitled Electricity made Plain and Useful by a Lover of Mankind and of Common Sense (1759).

Many years later, Edward Stillingfleet's Irenicon led him to decide that ordination (and holy orders) could be valid when performed by a presbyter (priest) rather than a bishop. Nevertheless, some believe that Wesley was secretly consecrated a bishop in 1763 by Erasmus of Arcadia, and that Wesley could not openly announce his episcopal consecration without incurring the penalty of the Præmunire Act.

In 1770, at the death of George Whitefield, Wesley wrote a memorial sermon which praised Whitefield's admirable qualities and acknowledged the two men's differences: "There are many doctrines of a less essential nature ... In these we may think and let think; we may 'agree to disagree.' But, meantime, let us hold fast the essentials..." Wesley was the first to put the phrase "agree to disagree" in print.

Wesley's prose, Works were first collected by himself (32 vols., Bristol, 1771–74, frequently reprinted in editions varying greatly in the number of volumes). His chief prose works are a standard publication in seven octavo volumes of the Methodist Book Concern, New York. The Poetical Works of John and Charles, ed. G. Osborn, appeared in 13 vols., London, 1868–72.

Later in his ministry, Wesley was a keen abolitionist, speaking out and writing against the slave trade. He published a pamphlet on slavery, titled Thoughts Upon Slavery, in 1774. To quote from one of his tracts against the slave trade: "Liberty is the right of every human creature, as soon as he breathes the vital air; and no human law can deprive him of that right which he derives from the law of nature". Wesley influenced George Whitefield to journey to the colonies, spurring the transatlantic debate on slavery. Wesley was a friend of John Newton and william Wilberforce, who were also influential in the abolition of slavery in Britain.

In spite of the proliferation of his literary output, Wesley was challenged for plagiarism for borrowing heavily from an essay by Samuel Johnson, publishing in March 1775. Initially denying the charge, Wesley later recanted and apologised officially.

Wesley's house and chapel, which he built in 1778 on City Road in London, are still intact today and the chapel has a thriving congregation with regular services as well as the Museum of Methodism in the crypt.

In 1784, he believed he could not longer wait for the Bishop of London to ordain someone for the American Methodists, who were without the sacraments after the American War of Independence. The Church of England had been disestablished in the United States, where it had been the state church in most of the southern colonies. The Church of England had not yet appointed a United States bishop to what would become the Protestant Episcopal Church in America. Wesley ordained Thomas Coke as superintendent of Methodists in the United States by the laying on of hands, although Coke was already a priest in the Church of England. He also ordained Richard Whatcoat and Thomas Vasey as presbyters. Whatcoat and Vasey sailed to America with Coke. Wesley intended that Coke and Francis Asbury (whom Coke ordained as superintendent by direction of Wesley) should ordain others in the newly founded Methodist Episcopal Church in the United States. In 1787, Coke and Asbury persuaded the American Methodists to refer to them as bishops rather than superintendents, overruling Wesley's objections to the change.

Following an illness in 1748 John Wesley was nursed by a classleader and housekeeper at an orphan house in Newcastle, Grace Murray. Taken with Grace he invited her to travel with him to Ireland in 1749 where he believed them to be betrothed though they were never married. It has been suggested that his brother Charles Wesley objected to the engagement though this is disputed. Subsequently, Grace married John Bennett preacher and resident of Chapel-en-le-frith and John's last visit to Chapel-en-le-frith on 3 April 1786 at the age of 86 was at Grace's request. Grace and John Bennet are buried in Chinley Independent Chapel in Chapel Milton.

Wesley practised a vegetarian diet and in later life abstained from wine for health reasons. Wesley warned against the dangers of alcohol abuse in his famous sermon, The Use of Money, and in his letter to an alcoholic. In his sermon, On Public Diversions, Wesley says: "You see the wine when it Sparkles in the cup, and are going to drink of it. I tell you there is poison in it! and, therefore, beg you to throw it away". However, other materials show less concern with consumption of alcohol. He encourages experimentation in the role of hops in the brewing of beer in a letter which dates from 1789. Despite this, some Methodist churches became pioneers in the teetotal Temperance movement of the 19th and 20th centuries, and later it became de rigueur in all.

Wesley's health declined sharply towards the end of his life and he ceased preaching. On 28 June 1790, less than a year before his death, he wrote:

Wesley died on 2 March 1791, at the age of 87. As he lay dying, his friends gathered around him, Wesley grasped their hands and said repeatedly, "Farewell, farewell." At the end, he said, "The best of all is, God is with us", lifted his arms and raised his feeble voice again, repeating the words, "The best of all is, God is with us." He was entombed at his chapel on City Road, London.

Numerous schools, colleges, hospitals and other institutions are named after Wesley; additionally, many are named after Methodism. In 1831, Wesleyan University in Middletown, Connecticut, was the first institution of higher education in the United States to be named after Wesley. The now secular institution was founded as an all-male Methodist college. About 20 unrelated colleges and universities in the United States were subsequently named after him.

In 1954, the Radio and Film Commission of the British Methodist Church, in co-operation with J. Arthur Rank, produced the film John Wesley. The film was a live-action re-telling of the story of the life of Wesley, with Leonard Sachs in the title role.

The 20th-century Wesley scholar Albert Outler argued in his introduction to the 1964 collection John Wesley that Wesley developed his theology by using a method that Outler termed the Wesleyan Quadrilateral. In this method, Wesley believed that the living core of Christianity was revealed in Scripture; and the Bible was the sole foundational source of theological development. The centrality of Scripture was so important for Wesley that he called himself "a man of one book"—meaning the Bible—although he was well-read for his day. However, he believed that doctrine had to be in keeping with Christian orthodox tradition. So, tradition was considered the second aspect of the Quadrilateral.

In 2002, Wesley was listed at number 50 on the BBC's list of the 100 Greatest Britons, drawn from a poll of the British public.

In 2009, a more ambitious feature film, Wesley, was released by Foundery Pictures, starring Burgess Jenkins as Wesley, with June Lockhart as Susanna, R. Keith Harris as Charles Wesley, and the Golden Globe winner Kevin McCarthy as Bishop Ryder. The film was directed by the award-winning film-maker John Jackman.

Wesley defined the witness of the Spirit as: "an inward impression on the soul of believers, whereby the Spirit of God directly testifies to their spirit that they are the children of God." He based this doctrine upon certain Biblical passages (see Romans 8:15–16 as an example). This doctrine was closely related to his belief that salvation had to be "personal." In his view, a person must ultimately believe the Good News for himself or herself; no one could be in relation to God for another.

Wesley was unhappy about the idea of field preaching as he believed Anglican liturgy had much to offer in its practice. Earlier in his life he would have thought that such a method of saving souls was "almost a sin." He recognised the open-air services were successful in reaching men and women who would not enter most churches. From then on he took the opportunities to preach wherever an assembly could be brought together, more than once using his father's tombstone at Epworth as a pulpit. Wesley continued for fifty years—entering churches when he was invited, and taking his stand in the fields, in halls, cottages, and chapels, when the churches would not receive him.

In the year of his ordination he read Thomas à Kempis and Jeremy Taylor, showed his interest in mysticism, and began to seek the religious truths which underlay the great revival of the 18th century. The reading of william Law's Christian Perfection and A Serious Call to a Devout and Holy Life gave him, he said, a more sublime view of the law of God; and he resolved to keep it, inwardly and outwardly, as sacredly as possible, believing that in obedience he would find salvation. He pursued a rigidly methodical and abstemious life, studied the Scriptures, and performed his religious duties diligently, depriving himself so that he would have alms to give. He began to seek after holiness of heart and life.