John Jay (1805–72) was a building contractor and, earlier, a skilled stonemason, who owned a construction company located in the central City of London within Metropolitan London, England, during the 19th century and its period of rapid civic and railway expansion in the middle of the 19th century. Jay's varied body of works included building the Victorian clock tower and city clock of the British Houses of Parliament after the Westminster Palace had been damaged by a fire in 1833 fire. Jay was also responsible for the construction of many smaller architectural projects, such as the notable Abney Park Chapel and the Trinity Independent Chapel.
John Jay was born in Norfolk, England, in January 1805. By 1826, he had moved to the village of Bethnal Green near the City of London, where he married Esther Wilson (1806–88) at St. Matthew's Church. By the late 1830s, Jay had his offices and workshops in the heart of the City of London at 65 London Wall. These appear to have been inheritance owned either by Jay alone, or else shared with close relatives, because in 1806, an older Mr. Jay, who was also a builder with an address at London Wall, had already rebuilt the building that was later renamed the "Adelphi Theatre", designed by the architect Samuel Beazley.
The first building known to have been built by John Jay was the Abney Park Chapel (opened May 1840). This project was soon followed by the Trinity Independent Chapel (opened 1841), both designed by the architect William Hosking, and St. Michael's Church in , designed by William Rogers.
During the 1850s, Jay won the contract for construction of the Victoria Towers and clock, and the Old Palace Yard frontage at the Houses of Parliament; and one for St. Olave's Grammar School. His other civic buildings included Andrew Reed's philanthropic ventures, the Infant Orphan Asylum at Wanstead (opened in 1843) and the so-called "Idiot Asylum at Earlswood" now the Royal Earlswood Hospital.