Walker first competed for Gibraltar at the
2000 IAAF World Cross Country Championships in
Vilamoura,
Portugal where he placed 158th in the
senior men's race in a time of 46:48 and finished 149th in the
men's short race in a time of 14:15. The following year at the
2001 Island Games in the
Isle of Man, Walker finished 4th in the
men's individual triathlon with a time 2:06:30. At the same meet, Walker also recorded a personal best and
national record time of 10:34.95 in the final of the
3000 m steeplechase. In July 2002, Walker made his debut at the
Commonwealth Games by competing in the men's
triathlon at the
2002 Manchester Games. He finished the course in 2:06:15.19 and placed 26th. Three months later, Walker competed in the
2002 Ironman World Championship in Hawaii. He finished 160th out of 280 in 35–39 age division and 767th out of 1605 overall with a time of 11:22:55. At the
2003 Island Games in
Guernsey, Walker won the silver in
men's individual triathlon and alongside
Harvey Gurry and
Anthony Perera finished 6th in the
team event. In November 2004, Walker underwent spinal surgery (an L5-S1 diskectomy) which caused permanent nerve damage to his right calf muscle. This injury made him change from triathlon to cycling. and with
Julian Bellido and
Sigurd Haveland finished 6th in
men's team time trial. At the
2006 Commonwealth Games in
Melbourne, Walker finished 34th in
men's road time trial with a time of 57:30.39. and in the triathlon where he finished 5th in the
men's individual triathlon with a time 2:05:35 and alongside
Edgar Harper, Sigurd Haveland and
Kevin Walsh finished 6th in the
team event. Walker qualified for the
2008 Ironman 70.3 World Championship held in
Clearwater, Florida. He finished 12th out of 159 in the male 40–44 age division and 179th of out of 1493 overall. At the
2010 Commonwealth Games in
Delhi, Walker finished 32nd in
men's road time trial with a time of 59:05.13. In May 2011, Walker competed in the 2011 Ironman Lanzarote in
Puerto del Carmen finishing 36th out of 299 in the male 40–44 age division and 173rd of 1469 overall in a time of 10:50:50. Cycling was dropped from the program for the
2009 Island Games, however, it returned in two years later at the
2011 Island Games in the
Isle of Wight where Walker contested five of six road cycling events. The following year, Walker first competed in the
Ironman European Championship in Frankfurt, Germany finishing 4th out of 502 in the male 45–49 age division and 134th of 2885 overall in a personal best time of 9:36:07. This result qualified him for the
2012 Ironman World Championship in Hawaii where he finished 58th out of 225 in his division and 578th out of 1984 overall with a time of 10:23:56. At the
2013 Island Games in
Bermuda, Walker failed to finish the
men's individual time trial but alongside
Mark Francis, Sigurd Haveland,
Robert Matto and
Sean Randall they finished in 7th place in 3:22:50.817 in the
men's time trial team award. The 2013 Games also saw Walker contest the triathlon where he finished in 4th place in the
individual event with a time 2:03:36 and won gold in the
team event with
Derek Barbara, Mark Francis,
Mark Garcia,
Andrew Gordon, Edgar Harper, Sigurd Haveland, Robert Matto,
Richard Muscat and Sean Randall. and later that year at the ITU World Championships in Edmonton, Canada Walker won Silver in the Sprint Distance event in the 45 - 49 age group with a time of 1:02:46 and Gold in the Standard Distance event in the 45 - 49 age group with a time of 2:01:07 At the 2015 NatWest Island Games in Jersey Walker finished in 5th place in the individual event and won Bronze
team event with Mark Francis,
Andrew Gordon, Edgar Harper, Robert Matto and Sean Randall. At the 2015 ITU World Championships in Chicago Walker won Bronze in the Sprint Distance event in the 45 - 49 age group with a time of 1:04:48 and finished 5th in the Standard Distance event in the 45 - 49 age group in a time of 1:50:33 ==Personal life==