Niniski was a bay horse with a white blaze and three white socks, bred in Kentucky by Caper Hill Farm Inc. Niniski was sired by Nijinsky, the Canadian-bred winner of the English Triple Crown in 1970 who went on to become an important breeding stallion, siring horses such as Ferdinand, Lammtarra, Sky Classic and Shahrastani. Niniski's dam Virginia Hills was a granddaughter of the Fashion Stakes winner Ridin' Easy, herself a descendant of the Prix de l'Arc de Triomphe winner Pearl Cap, making her a distant relative of Pearl Diver, Belmez, Lypharita (Prix de Diane), Fine Pearl (Prix de Diane) and Yelapa (Grand Critérium).
