William Law was born in 1686 at King's Cliffe, Northamptonshire, the son of a grocer of respectable standing. He received an excellent education at Grantham School and at Emmanuel College, Cambridge, where he developed the classical learning and theological acuity that would mark his mature work. After ordination and election as a fellow of Emmanuel College, he served as chaplain and tutor—positions that promised a distinguished academic ecclesiastical career.

His life took a sudden and defining turn in 1714 when he refused to take the oath of allegiance to George I, declaring his conscience bound to the Stuart line. This act of principled nonjury cost him his fellowship and any possibility of preferment in the Church of England. Rather than retreat into obscurity, Law relocated to London, where he supported himself as a private tutor. He served for several years in the household of Edward Gibbon, grandfather of the historian, as chaplain and domestic tutor—a position that provided both security and the leisure to write.

During this period of apparent restriction, Law produced his greatest works. A Treatise upon Christian Perfection appeared in 1726, but it was A Serious Call to a Devout and Holy Life (1728) that would reshape Anglican spirituality and influence the broader Protestant world. The Serious Call is remarkable for its combination of theological sophistication, moral clarity, and vivid character portraiture. Law populated its pages with satirical yet sympathetic portraits—Flavia the fashionable woman, Calidus the businessman preoccupied with worldly gain, Miranda the truly devout—showing how ordinary Christians either evade or embrace the radical demands of Gospel charity and holiness.

The book's impact was immediate and profound. Samuel Johnson, then a young man adrift in spiritual uncertainty, credited reading the Serious Call with making him 'think in earnest of religion' for the first time. John Wesley reported that Law's teaching shaped his understanding of holiness and Christian perfection, though Wesley later diverged from Law's theology on several points. George Whitefield acknowledged Law's formative influence on his own spiritual awakening. The Serious Call became standard reading for Anglican ordinands, devout laity, and educated dissenting ministers throughout the eighteenth and nineteenth centuries. Its influence extended to figures as diverse as Samuel Taylor Coleridge and the Tractarian theologians of the nineteenth century.

In his mature years, Law returned to King's Cliffe, where he lived with extraordinary simplicity and ascetic discipline. He devoted himself to prayer, charitable work among the poor of the parish, and deep study of the German mystical theologian Jakob Böhme. This turn toward mysticism puzzled some contemporaries who had known him only through the moral and intellectual rigor of the Serious Call. To Law, however, there was no contradiction: the God who demands holy living and moral transformation is the same God who draws the soul into deeper union and contemplative knowledge. His later writings—The Spirit of Prayer (1749) and The Spirit of Love (1754)—explored this interior dimension of faith, seeking to show how systematic prayer and mystical awareness interpenetrate.

Law died peacefully at King's Cliffe on April 9, 1761, in his seventy-fifth year, having lived as a living embodiment of the devout and austere Christianity he had commended to others.