John Platt was the second son of Henry Platt and the brother of Louisa Platt. He married Alice Radcliffe, the daughter of Samuel Radcliffe in 1842.
John Platt developed Platt Bros into a very successful engineering company making textile machinery.
He became the senior partner of the firm after the deaths of his father in 1842, elder brother Joseph (1815-1845), and Elijah Hibbert in 1846. He became a member of the Manchester Royal Exchange in 1842. In 1854 John and his brother James acquired Hibbert's share in the business and the firm became Platt Bros and Co.
John Platt's mechanical ability became apparent after taking out his first patent in 1846. After the statutory restrictions on export of machinery were abolished in 1843 he became the prime mover in operations of the firm and established firm's supremacy in markets of Europe. During 1850s firm became largest textile machinery maker in the world. Number of employees increased from 500 in 1843 to 7000 in 1872.
He became chairman of Oldham Liberal Party in 1847 and became mayor.
A convinced radical in politics he served as MP for Oldham from 1865 until his death.
He had become a member of the Anti-Corn Law League in 1843 and remained a lifelong advocate of free trade.
In 1857 he acquired a country estate at Bryn-y-Neuadd, Llanfairfechan and added much larger neighbouring estate of Gorddinog in 1869.
1862 London Exhibition: Catalogue: Class 7.: Platt Brothers and Co: https://www.gracesguide.co.uk/1862_London_Exhibition:_Catalogue:_Class_7.:_Platt_Brothers_and_Co
On 18 May 1872 he died suddenly from typhoid in Paris at the age of 54.
In 1878 a bronze memorial was inaugurated outside the town hall, giving Oldham its second public statue.
Platt, John Esq.
Effects under £800,000
The will of John platt late of Werneth Park, Oldham in the county of Lancaster and of Bryn-y-neuadd in the county of Caernarvon, Esquire who died 18 May 1872 at the "Hotel Meurice" Rue Rivoli in the city of Paris was proved at Manchester by Henry Platt of Gorddinog in the parish of Aber in the county of Caernarvonshire Esquire, Samuel Radcliffe Platt of Werneth Park Machine Maker, Frederick Platt of Werneth Park Machine Maker the sons, Thomas Hardcastle Sykes of Cringle House, Cheadle in the County of Chester, Bleacher, and Joshua Walmsley Radcliffe of Holly Lea near Rochdale in the county of Lancaster, Woolen Manufacturer, the Executors.