He was born at Wirksworth on 12 June 1803. At 15 he entered his father's hosiery business, which was later transferred to Lea. It was failing when too over in 1827, but by the time of his father's death in 1840, there had been a switch from cotton to wool and John Smedley was very wealthy. In early life he was an evangelical Anglican, with a dislike of Dissent, and even more so of WM. In 1846 he married the daughter of the vicar of Wirksworth, was taken ill on honeymoon and on his return home found that his Methodist visitors were more solicitous of his spiritual as well as his physical health. While at Ilkley for hydropathic treatment, he underwent a profound spiritual conversion and on his return to Matlock began associating with the WMs. At his Lea Mills he paid good wages, had a paternalistic attitude to his employees and started a free hydropathic hospital for them. In 1853 this led to the building of Smedley's Hydro. It was run on religious lines, with tobacco and alcohol prohibited.
After 1849 his sympathies were with the Wesleyan Reformers, and he designed and built six chapels for them in the Cromford (later Matlock) UMFC circuit: Birchwood (1849), Higham (1852), Holloway (1852), Bonsall (1852), Butts Chapel, Ashover (1857), and Matlock Bank, close to his hydro. Each had the unusual feature of a bell. He also gave generous support to chapels of the Primitive Methodists and Original Methodists in the area. He produced a liturgy 'purging the Church Prayer-Book of all objectionable matter, all unsuitable rites and ceremonies, and all heterodox doctrines, of which he had long complained so bitterly, if so unsuccessfully'. The now ruined Riber Castle, built as his home in the 1860s, is alleged to have cost £60,000. He died there on 27 July 1874.