After enjoying a prolific school cricket record at The King"s School, Rochester, Walker made his first appearance for Kent in a second-team match against Lancashire in 1990. He continued to play in the second eleven for two seasons, after which he was called up to the England Under-19 squad for their tour of Pakistan. The tour started poorly for Walker, only making one score of note in the "Test" series.
However, he managed to average 48.00 in the limited-overs games that followed.
He continued to appear for the England under-19 team until the end of the West Indian tour of England, by which time he had earnt an average of 42.07 from 12 youth Tests. Walker was selected for Kent"s first-team for the first time during the side"s 1993 pre-season tour of Zimbabwe.
Against a Zimbabwean "B" team, Walker scored 23 not out and 16 in a drawn match. Despite the promise shown on the tour, Walker would not play for the first-team for another fifteen months.
His List A debut came on 17 July 1994, in a Sunday League match against Worcestershire.
In nine matches that season, Walker averaged 23.37. In first-class cricket, Walker has had three seasons where he has finished with a batting average of over fifty. In 1996, 2004 and 2006.
1996 saw Walker hit the highest score of his career to date, on his way to 606 runs at an average of 60.60.
Against a Somerset attack without Andrew Caddick, Walker compiled 275 not out in nine-and-a-half hours before his captain Trevor Ward declared the innings at 616/7. The Daily Telegraph"s Christopher Martin-Jenkins wrote of the innings: "lieutenant was an innings of style and substance, memorable for powerful driving through the off-side and hearty pulling whenever a persevering but ordinary Somerset attack became impatient with line and length and tried to extract a spring in the pitch which simply was not there." lieutenant remains the highest score by a Kent batsman at the Street Lawrence Ground.
Despite the talent he had shown during his innings against Somerset, he found the next few seasons difficult. In an interview with All Out Cricket magazine, he said "I’d had a bit of first team cricket, and was dropped and managed to work my way back into the team in the second half of the year but just couldn’t get it right." Foreign four seasons, between 1997 and 2000, Walker consistently averaged in the mid-twenties, scoring just one century in the process.
Since then, he has scored over one thousand runs in a season on three occasions.
Walker"s most productive season in terms of run-scoring was 2006, in which he scored 1,419 runs at the average of 61.19. In the game against Lancashire that year, he came close to adding a second career double-century to his name. However, he was dismissed on 197, run out after collapsing with cramp.
Walker was appointed List A captain of Kent for the second half of the 2005 season, following the resignation of David Fulton.
However, he was unable to lead the team any higher than eighth in the second division of the Pro40 League. In 2007, Walker hit the highest score of the innings in Kent"s victory over Gloucestershire in the Twenty20 Cup Final.
However, after finding first-team opportunities limited during 2008, he was released by Kent and signed for Essex on a two-year contract. In the winter of 2011, Graham Gooch stepped down in his role as Essex Batting Coach to work full-time with England.
Walker was appointed as the Batting Coach.
lieutenant was also confirmed that he would keep his player registration, although he would only play in the event of many injuries. In April 2014, Walker re-joined Kent as an assistant manager having left Essex.