John was baptised in Cottisford, an Oxfordshire parish a few miles west of Buckingham on 23rd October 1748, the son of John and Joanna Westcar. John senior was a wealthy grazier (a farmer who reared cattle or sheep for market) whilst Joanna came from a prominent Northamptonshire family and was Great-Aunt to Lord Sidmouth, the Prime Minister from 1801 to 1804.
John junior followed in his father’s footsteps and also became a grazier. He spent his early adulthood at Mixbury in Oxfordshire where his father was farming when he died in 1784. John married Mary Hedges of Creslow, daughter of Thomas Hedges a grazier, at Cublington parish church on 22nd March 1780 by licence. The marriage licence bond records John as being a Gentleman of Mixbury. The Hedges had farmed at Creslow for much of the 18th century and it seems that following John’s marriage to Mary, he took over as grazier at Creslow and leased several hundred acres of land from the Earl of Clifford who was the lord of the Manor of Creslow at the time.
The Creslow pastures were renowned for their exceptional fertility and were considered to be the finest in the county. At the dissolution of the Monasteries under Henry VIII, the Manor of Creslow was then in the hands of the Knights Hospitaller. The King appropriated the land and the pastures were used for feeding cattle for the Royal household up until the Commonwealth under Oliver Cromwell. The Cliffords subsequently acquired the land in the 1670s.
The Westcars lived in the 14th century manor house at Creslow, one of Buckinghamshire’s oldest continually inhabited buildings. Originally there was a church at Creslow which adjoined the manor house but during Queen Elizabeth's reign, services ceased to be performed and it later was used as a dovecot. John Westcar adapted it to serve as a coach-house by the insertion of partition walls and upper floors.
John specialised in breeding Hereford cattle and as early as the 1770s he attended the Hereford fairs to purchase cattle which he bred on the Creslow pastures and sold at markets including Oxford and London. On occasion it was reported that he visited the fairs with Francis the fifth Duke of Bedford who was greatly interested in agriculture and later became the first president of the Smithfield Club. The pastures included the “Great Field” which comprised 310 acres of undulating ground and in the summer months John reportedly kept over 200 large oxen and up to 500 sheep and lambs and around 20 mares and foals. At the time, there were large elm trees on one side which gave shade to the animals.
He was one of the founding members of the Smithfield Cattle and Sheep Society (later known as the Smithfield Club and now as the Royal Smithfield Club) which was formed in 1798 with the aim of improving and promoting the breeding of cattle, sheep, pigs, poultry and other livestock. At the first annual Royal Smithfield Show held in 1799 he won first prize for one of his oxen which sold for 100 guineas (over £5000 in today’s money) and reportedly weighed in at nearly 250 stone. Some of the oxen were fed on turnips and hay, (grass fed) whilst others were fed on oil cake and corn. Newspapers at the time reported that he regularly won prizes at shows over the next 20 years (at least 42 in total at Smithfield).
John pioneered the transport of cattle by canal. The opening of the Grand Junction Canal (later the Grand Union Canal) as far as Marsworth by 1799 made it a much easier method of transporting cattle to the London markets rather than using the old drovers’ roads although in the early days transportation by canal had its problems. Dry summers led to shortage of water in the canal and it was reported in The Morning Chronicle in 1802 that “Mr Westcar’s large oxen were intended to come from nearest point of the Grand Junction Canal to his farm, then by a barge to Paddington Wharf, but the shortness of the water on the summit at Tring, by which the public have, during this and the late summers suffered so much, prevented it, and the oxen were obliged to be driven to Two Waters wharf [Hemel Hempstead], where they were put into a barge and conveyed to Paddington.”
In 1831 John had his portrait painted by artist and engraver Charles Turner who had been appointed "Mezzotinto Engraver in Ordinary to his Majesty" in 1812. The portrait is now in a collection at the National Portrait Gallery.