After serving his apprenticeship in Worcestershire's Second XI and for the county's Board XI in the 38-County Cup for a couple of years, Kabir Ali made his first-class debut in a drawn game against Middlesex in September 1999. He bowled respectably enough, taking 2–36 and 1–22, but the match's lateness in the season robbed him of the chance to push for a regular place in the first team. Despite several appearances in the Benson & Hedges Cup in April 2000, including an impressive 4–29 on List A debut, Kabir spent most of the first part of that season still in the second team, although by the summer he had pushed his way into the full XI. Also in 2000, Kabir was awarded the NBC Denis Compton Award for the most promising young Worcestershire player.

Over the following few years, Kabir gradually established himself as a hard-working bowler who was dedicated to his craft. His best period to date has been 2002-3; he took 138 first-class wickets in those two English seasons, including eight five-wicket innings hauls. International recognition first came during the 2002-3 winter, when he was invited to tour Australia with the ECB National Academy. It was thus unsurprising that he was selected to play for England in 2003, making his One Day International debut against Zimbabwe that July – although the game was a washout and Kabir had no chance to make an impression.

He was also selected for the Fourth Test against South Africa at Headingley in August 2003, taking a wicket in his first over (Neil McKenzie, caught behind by Alec Stewart off Kabir's fifth ball). He took five wickets in the match: 3–80 in the first innings and 2–56 in the second, including the key wicket of Gary Kirsten (for 130 and 60) in both innings. Nonetheless, England were soundly beaten and the selectors rang the changes, bringing in Steve Harmison and Ashley Giles for Kabir and James Kirtley. The Headingley match was Kabir's solitary Test appearance, although he made a number of further appearances at ODI level. His greatest success came against South Africa in 2004/05, when he took more wickets (13) than any other England bowler, and at Bloemfontein somehow conjured a tie from nowhere.

Kabir first came to national prominence when he took a second-innings 5–48 (and eight wickets in the match) against the touring Zimbabwe side in May 2003; in a precursor to his final-over heroics at Bloemfontein, Kabir claimed the final two wickets with the scores level to tie the match. Kabir's life was touched by tragedy in July 2003, when his two-week-old nephew died. However, his father wished him to play for Worcestershire against Derbyshire a few days later, and he put in a magnificent display. After a quiet first innings with the ball, he scored a quickfire 68, putting on 104 with Steve Rhodes for the eighth wicket to help rescue his team from deep trouble at 190/7, and then ripped through the Derbyshire batting line-up to take 8–53, at the time the best innings analysis of his career. Thanks to Kabir's heroics, Worcestershire won the game by an innings. Kabir further demonstrated his batting credentials in September 2003, hitting 92 from 93 balls in a 45-over National Crick