After his parents moved to Ripley, Surrey, he attended the George Abbot School in Guildford, completing his GCSEs and A-levels. The Giles family was heavily involved with Ripley Cricket Club: Ashley's father, brother Andrew, cousins and uncles all played for the club, as did both paternal and maternal grandfathers previously. Giles soon moved into the Saturday 2nd XI, opening the bowling with close friend Ian Ward. At this stage, both players were aspiring fast bowlers, and a deadly force for Surrey Under-9s. Giles moved to Guildford Cricket Club, working under coach Brian Ruby alongside future professionals Darren and Martin Bicknell. Giles advanced through the county age-groups, and toured Barbados with Surrey Young Cricketers in 1990/91. While at Guildford, an injury forced Giles to try bowling spin, which brought him some success. Giles made his debut for the Surrey Second XI in 1990, and was named Surrey Young Cricketer of the Year in 1991. The following season, he played one further match for Surrey but they were unable to offer him a professional contract. After an initial trial with Dennis Amiss, Giles was awarded a one-year contract Warwickshire County Cricket Club. Between 1992 and 1995, Giles played the majority of his games for Warwickshire Second XI, scoring over 2,500 runs and taking 165 wickets in this period. He made his first-class debut for Warwickshire against Kent in May 1993; his second match was against Durham later that season. In September 1993, he made his List A debut against the touring Zimbabweans, his first wicket being that of Grant Flower, although it would not be until the tail-end of the 1995 season before Giles began to cement his place in the Warwickshire side taking 16 wickets at an average of 22.12 (in 6 matches). In 1996 Giles won the NBC Denis Compton Award, and before his debut for the full national side in 1998 he toured Australia, Sri Lanka and Kenya with the England A team. Giles played winter cricket in South Africa for Vredenberg & Saldanha (1992–95) and Avendale (1995–96). On 2 July 1998, Giles made his Test debut against South Africa, and took 1 for 106 in 36 overs. He then went on to tour Australia in the One Day squad. On 31 December, it was announced that Giles was to step out of the One Day match between the ODI squad and the Bradman XI, and into the Test squad for the final Test match in Sydney.