Born in Milton Keynes, Buckinghamshire, Hildreth attended Millfield, a private school in Street, Somerset described as a "great nursery of the game [of cricket]".

[5] In July 2002, Hildreth made his first appearance for the Somerset Second XI, replacing Peter Trego who, after scoring 188 runs in the first-innings, left the match due to being called up to the first-team.

Hildreth bowled 13.1 wicket-less overs during Warwickshire Second XI's first-innings, and scored 32 in Somerset's second-innings, as they lost by an innings.

[6] The following month, he made his List A debut, representing Somerset Cricket Board against Cornwall in the first round of the Cheltenham and Gloucester Trophy.

[11] In the nine National League matches Hildreth played in 2003, he scored 120 runs at an average of 15.00, with a high-score of 30 against Lancashire at the County Ground, Taunton.

[12][13] Playing in his (and Somerset's) first County Championship match of the 2004 season, Hildreth made his debut first-class century in the first-innings against Durham, scoring 101 in an innings described by team-mate Peter Bowler as "attractive but very orthodox".

[30] He remained with the squad for the one-day series, but only managed to score four in his only batting appearance, as both the second and third ODIs were washed-out.

[37] In the second Test, played at Hildreth's home ground in Taunton, he scored 210 in "a near flawless innings with an explosive conclusion"[38] to help England to an eight wicket victory.

[39] The score, at the time the sixth highest in youth Tests,[40] was described by Bangladesh's coach Richard McInnes as "one of the best innings I have ever had the pleasure of seeing.

[41] In the English winter of 2007–08, Hildreth was included in the England Performance Programme XI to train in India, playing two matches against 'Madras Rubber Factory'.

[45][46][47] Hildreth was used as a substitute fielder throughout the 2005 Ashes series and took a catch to dismiss Ricky Ponting in the first Test at Lord's off the bowling of Matthew Hoggard.