Sir Percy dam Percy's Lass won the Group 3 September Stakes in 1988 (and subsequently died of colic when Sir Percy was a foal. Sir Percy was the last of her offspring) and his damsire Blakeney won the Epsom Derby himself in 1969. Sir Percy was named after Sir Percy Blakeney, the hero of the novel "The Scarlet Pimpernel". In November 2003 Sir Percy was sent as a weanling to the Tattersalls sales. He was bought for 20,000 guineas by Will Edmeades bloodstock, acting on behalf of Anthony Pakenham. Pakenham bought the colt as compensation for losing a National Hunt Horse. Sir
Sir Percy Percy was sent into training with Marcus Tregoning at Lambourn, Berkshire. He was ridden in all his races by Martin Dwyer. Sir Percy was undefeated as a two-year-old, winning all four of his races. He made his debut in a maiden race at Goodwood on 28 May. He started at odds of 8/1 and finished strongly to win by one and three quarter lengths. Four weeks late he started 7/4 favourite for a minor stakes race at Salisbury and won by one and a quarter lengths from . On 27 July Sir Percy completed his hat trick and recorded his