Bred and originally trained in Yorkshire, he was unbeaten in two races as two-year-old in 1824, including the Champagne Stakes and won the York version of the St Leger the following spring.

Memnon was a "long, loose, big and leggy"[1] bay horse with one white foot bred at Bishop Burton in Yorkshire by Richard Watt.

Ridden as usual by Bill Scott, he started the 3/1 favourite against twenty-nine colts and fillies, the largest field assembled for the classic up to that time.

[15] For the 1827 season, Memnon was moved south to be trained at Newmarket by William Chifney, and was ridden in most of his subsequent races by his new trainer's brother Samuel Chifney, Jr. On 15 May at Newmarket Racecourse, Memnon made his five-year-old debut in a 1,000 guinea match race over ten furlongs in which he easily[16] defeated Lord Exeter's Enamel, the winner of the 1822 2000 Guineas.

Ridden by Sam Chifney, he started 1/2 favourite for the two and a half mile race and won impressively[18] by two lengths[19] from King George IV's horse Mortgage and three others.

[20] In autumn, Memnon appeared at the Doncaster St Leger meeting for the fourth year in succession, but on this occasion, he failed to win a race.

[21] Two days later he started second favourite for the Doncaster Cup over two miles five furlongs against a field which included Fleur-de-Lis, Actaeon and the 1826 St Leger winner Tarrare.

[22] Memnon was scheduled to run a three-mile match race against The Alderman at Newmarket in October, but his opponent failed to appear, leaving Lord Darlington to collect a 250 guineas forfeit.

[24] In October Memnon was scheduled to challenge for The Whip, a silver trophy which was said to incorporate hairs from the tail and mane of Eclipse,[25] but he failed to appear for the race, allowing Colonel Wilson's Lamplighter to claim the prize.