Kirtley first came to prominence when playing for Mashonaland in Zimbabwe in 1996/97 against the touring England team and he claimed the dismissals of Michael Atherton and Nasser Hussain as he took seven wickets in the game.
He was awarded his county cap in 1998 and in 1999/2000 was a replacement on England’s A tour of Bangladesh and New Zealand after being called up when Steve Harmison withdrew.
Kirtley has enjoyed many happy days bowling at Hove and has over 400 first-class victims of which 75 were in the 2001 domestic season.
While representing England in the 2002 NatWest Series with India and Sri Lanka he took a remarkable catch against India at Lord’s which will linger in the memory for many years to come.
In 2003, after many false starts, he finally made his Test debut against South Africa at Trent Bridge and claimed 6-34 in the second innings to earn the man-of-the-match award.
He also helped Sussex win the Frizzell County Championship for the first time that summer.
In the 2005 summer, Kirtley took 31 wickets in Sussex's successful bid for the Division Two totesport league title, and 59 wickets to see the county come third in the championship.
He was suspended in October 2005 because his bowling arm exceeded the 15 degrees of 'elbow extension' permitted for a fast bowler but he remodelled his action and was cleared in March 2006.
His loyalty to the county was rewarded when he was awarded a benefit in 2006 and he helped Sussex to the Liverpool Victoria County Championship and took five wickets in the C&G Trophy Final to secure a narrow victory over Lancashire.
In December 2006 he signed a contract extension to keep him at Sussex until the end of the 2008 season.
Kirtley was called up to join England A’s tour of Bangladesh in February 2007 as a replacement for the injured Amjad Khan, and was named in England's 15-man squad for the World Twenty20 in South Africa.
He rarely played as Sussex recorded their second successive championship title in 2007, but was an ever-present member of their one-day squad, topping the county's bowling averages in all competitions.
He signed a new one-year contract at the end of the 2008 season, when he was the county’s leading wicket-taker in the NatWest Pro40 with 11 victims.