Although he failed to reproduce his best form in the autumn of his three-year-old season, he returned in 1861 to win his first four races including the Ascot Gold Cup.

He was bred by Benjamin Plummer who had difficulty finding a buyer for the young horse[2] as a yearling at the Doncaster sales, before selling him privately for £350 to the trainer Mathew Dawson.

This view was supported by the testimony of Mathew Dawson, who was working at the stud at the time of Thormanby's conception: he reported that Alice Hawthorn had rejected Melbourne, but been receptive to Windhound.

Thormanby, however, had been performing exceptionally well in training, notably when giving thirteen pounds and a decisive beating to a good colt called Northern Light.

Dawson did, in fact, fear that attempts would be made to deliberately injure or "nobble" Thormanby and took steps to protect him, including switching his jockeys' racing colours at the last moment to confuse any potential assailants.

[9] At Epsom on 23 May, Thormanby impressed observers when he appeared in the paddock before the Derby: his coat was "like a mirror" and as he galloped to the start, he "hardly seemed to touch the ground.

Thormanby held third place turning into the straight but faded in the closing stages and finished fifth, four lengths behind the winner St Albans.

He was held up in the early stages before making a strong challenge in the straight, but was beaten three lengths by Sabreur, to whom he was conceding seven pounds.

Thormanby's four-year-old season began at Newmarket in April, when he won the Claret Stakes, finishing thirty lengths clear of his two rivals.

Thormanby raced lazily, so that Custance had to "waken him up" by using his spurs, but in the straight he produced a strong run to overtake Parmesan and easily held the late challenge of the filly Fairwater to win by two lengths.

In May 1886 The Sporting Times carried out a poll of one hundred racing experts to create a ranking of the best British racehorses of the 19th century.

[1] Thormanby's tail was mounted and fashioned into a whisk which was hung in the hall of Mathew Dawson's Heath House at Newmarket.