Bred by Dennis O'Kelly, Jupiter was produced by the famous Old Tartar Mare bred by Edward Leedes, and was full brother to Mercury (ch c 1778), Queen Mab (ch f 1785) and Volunteer (ch c 1780) among others. Queen Mab was described as a chestnut with a white mane and tail, which might apply to Jupiter as well. Cook notes that the Stubbs painting of him which hung at Elsenham Hall shows his coat changing to bright cream with a black mane [A History of the English Turf 2:332], which seems a curious observation. Perhaps he meant to say "with a white mane," or perhaps he was describing the process of a palomino turning grey, which, to those unfamiliar with it, is a curiosity in itself. Jupiter himself was described as standing 15.2 hands and of great length with proportionate bone.

Lightly raced for three years by Dennis O'Kelly, he won three of his eight starts, after which he was purchased by Colonel Thomas Thornton. He was in the stud from 1790 to 1802 at Thornville Royal, near Boroughbridge, Yorkshire, where he sired mostly hunters, although he did get two mares that bred on. Jupiter Mare (b f 1792) was the ancestress of such winners as (1) The White Knight (b c 1903 Desmond) who won the Ascot Gold Cup twice, the Coronation Cup twice, and the Ascot Gold Vase and Goodwood Cup, (2) the stallion Dinneford (br c 1902 Dinna Forget) who won the Princess of Wales's Stakes, and (3) Grakle (b c 1922 Jackdaw) who won the Grand National Steeplechase. Jupiter Mare (f 1792) was the dam of the stallion Whitworth (b c 1805 Agonistes) who in turn sired Lady Eliza (b f 1813), ancestress of Newminster (b c 1848 Touchstone). Jupiter also sired Sir Walter* (b c 1793).