Bay Middleton was bred at Middleton Stoney, Oxfordshire, by George Child Villiers (1773-1859), 8th Viscount Grandison and 5th Earl of Jersey, a prominent early 19th century breeder and owner, who was twice appointed Master of the Horse to Queen Victoria, in 1841 and 1852. His other classics winners included the Two Thousand Guineas winners Riddlesworth (ch c 1828 Emilius), Glencoe (ch c 1831 Sultan), Ibrahim (br c 1832 Sultan) and Achmet (b c 1834 Sultan), the Derby winners Middleton (ch c 1822 Phantom) and Mameluke (b c 1824 Partisan), the One Thousand Guineas winner Charlotte West (ch f 1827 Tramp), and the One Thousand Guineas and Oaks winner Cobweb. Cobweb was the dam of Bay Middleton and Achmet as well as the One Thousand Guineas winner Clementina (b f 1844 Venison). Lord Jersey is also the breeder of record for The Princess (ch f 1841 Slane) who won the Oaks for Colonel Anson. Bay Middleton was later purchased by Lord George Bentinck (1802-1848), son of the 4th Duke of Portland, for £4000.

Bay Middleton, who stood sixteen hands, one and a half inches, was noted for his good quarters, arched neck and indomitable courage, although he was beset by a wonky foreleg. A difficult youngster who "bolted with everybody," he was eventually calmed by the careful riding of James Robinson.

Running only as three year old he was called "Brother to Nell Gwynne" in his first engagement, the Riddlesworth Stakes at Newmarket, Craven, which he won in the "commonest of canters". He remained undefeated the rest of the year, winning the Two Thousand Guineas Stakes at Newmarket, First Spring, the Derby Stakes at Epsom, the Buckhurst Stakes at Ascot, and, despite a battle with the game Elis, the Grand Duke Michael Stakes at Newmarket, First October. He also collected £150 for a walk-over and beat Muezzin with "ridicuolous ease" in a match for 300 guineas whilst conceding him nearly a stone. He remained in training for several more years although his leg prevented him from starting and he finally broke down in 1838.

He was not initially successful in the stud and at one point covered at the Turf Tavern in Doncaster for only 10 guineas. He did, however, get the Derby winner Andover (b c 1851), the One Thousand Guineas winner Aphrodite (br f 1848), the Two Thousand Guineas winner The Hermit (br c 1851) and the Derby and St Leger winner The Flying Dutchman (br c 1846), the latter from Barbelle and responsible for the perpetuation of the Herod sire line in France. Bay Middleton was a Champion Sire in 1844 and 1849. He died at Danebury, near Stockbridge, Hampshire, in November of 1857.