Bowes was the illegitimate, though much-loved son of the tenth earl of Strathmore (who finished and consecrated the exquisite Gibside Chapel in 1812). Augustus Hare calls the earl 'a very agreeable and popular man, but by no means a moral character.' Hare goes on:

'Living near his castle of Streatlam was a beautiful girl named Mary Milner, daughter of a market gardener at Staindrop. With this girl he went through a false ceremony of marriage, after which, in all innocence, she lived with him as his wife. Their only boy, John Bowes, was sent to Eton as Lord Glamis. On his deathbed, Lord Strathmore confessed to Mary Milner that their marriage was false and she was not really his wife. She said: "I understand that you mean to marry me now, but that will not do: there must be no more secret marriages!" She had everyone within reach summoned to attend the ceremony, had him carried to church [in London] and was married to him before all the world. Lord Strathmore died soon after he re-entered the house, but he left her Countess of Strathmore. It was too late to legitimise John Bowes.'

Bowes' wealth derived from the internationally-famous Streatlam stud, and the rich coal-seams below the Gibside estate. The stud never had more than ten brood mares at one time, but such was the judgment of Bowes and his trainer John Scott, that he bred four Derby winners in twenty years. The last of these, West Australian, was the first-ever winner of the triple crown in 1853. These achievements place Bowes among the most successful owners in British racing history, Incidentally, the dam of Eclipse, the most famous racehorse in the world, was bred at Windlestone in County Durham.
Bowes' illegitimacy was a social disability in England, and in 1847, he moved to Paris, a city he had been visiting since 1832. He had met William Thackeray there and given him financial assistance. Bowes, in fact, was in favour of the reform Bill, the abolition of slavery, religious toleration, and the promotion of the 'moral, social and intellectual advancement of the people'. He represented South Durham from 1832 until 1847, and even after his departure for France, was very keen to keep up with local events as reported in the Teesdale papers.
In 1852, Bowes married his mistress, the French actress Benoite-Josephine Coffin-Chevalier (1825-74), the daughter of a clockmaker. It was she who was behind the project of the astonishing chateau-like Bowes Museum at Barnard Castle. The project was largely educational as the couple wanted to introduce the wider world to the people of Teesdale and the North of England in general. To this end, they collected as wide a variety as possible of materials and techniques, objects and artists. Every European country in 1870 is represented in the collections. Building began in 1869, the year after Josephine became the Countess of Montalbo. Neither Bowes nor his wife lived to see the building opened in 1892, but the arrangement of contents is theirs.
The Bowes Museum is regarded as the most important collection of European decorative art after the Victoria and Albert Museum in London. Its pioneering Spanish collection is the largest outside the National Gallery and it acquired a Tiepolo at least ten years before the National gallery did. The Bowes also has the largest collection of French pictures in the British Isles, two splendid Canalettos, two Goyas and an El Greco. Perhaps the most celebrated attraction is the wonderful silver swan automaton. The famous American humorist Mark Twain saw the swan at the Paris International Exhibition of 1867, and described it in his The Innocents Abroad. Not far away at Preston Hall Museum, there is an outstanding French painting The Dice Players by the rare 17th century artist Georges de la Tour. The work is of national importance and was shown at the Royal Academy in the Art Treasures of England exhibition of 1998.