Lieutenant-Colonel John By was born in 1779 and baptised at St Mary Lambeth on 10 August 1779, the second son of George By and his wife Mary, née Bryan. They lived in Archbishop's Walk, Lambeth, and all held positions at the Customs House where his father was chief searcher. After passing through the Royal Military Academy at Woolwich, John By was commissioned as a second lieutenant in the Royal Artillery on 1 August 1799 and transferred to the Royal Engineers on 20 December. He was commissioned as a lieutenant on 18 April 1801 and in the same year married Elizabeth Johnson Baines, daughter of Cuthbert Baines of Penzance. In August 1802 John By went to Canada, where he was involved in repairs to the Cascades bateaux canal on the St Lawrence and superintended the construction of four Martello towers for the defence of Quebec. In 1811 he was in Portugal and took part in the first seige of Badajos and in January 1812 he took charge of rebuilding the gunpowder works at Waltham Abbeyand he also became engineer-in-charge of the works at Enfield, Faversham and Purfleet.
John's first wife Elizabeth died in 1814 of cholera and on 14 March 1818 he married Esther, daughter of John March of Harley Street and granddaughter of John Raymond Barker of Fairford Park, Gloucestershire. He remained in charge of the gunpowder works until August 1821 when he was retired on half pay. In January of the previous year John By had purchased Shernfold Park in Frant from James Cranbourne Strode; the house had been built in 1790 by Charles Pigou, a gunpowder manufacturer.
In April 1826 John By went again to Canada, having been selected to design and construct a military canal between the Ottawa River and Lake Ontario, safe from attack by the Americans. The town which grew up around his headquarters, originally named Bytown, was renamed Ottawa after the union of Upper and Lower Canada. The story of this prodigious feat of engineering, of the parliamentary censure of John By, his recall in October 1832 and the subsequent committee of enquiry are told in "Building the Rideau Canal: A Pictorial History" (Robert W Passfield, Parks Canada, 1982) and is depicted on History of the Rideau
In the remaing few years prior to his death on 1st February 1836, John By extended the Shernfold Estate by purchasing numerous adjacent properties. He is buried at St Albans Church in Frant.
In 1924 the Rideau Canal was designated a Canadian historical site and in June 2007 the Rideau Canal was inscribed on the World Heritage List by UNESCO's World Heritage Committee. The Rideau Canal World Heritage Site includes the Rideau Canal, Fort Henry and the Kingston Fortifications. The Canal extends 202 kilometres from Ottawa in the north to Kingston Harbour on Lake Ontario in the south.