In 2008 summer, after a short period at CD Quintanar del Rey,[3] Walker joined Atlético Zabal (Real Balompédica Linense's farm team), but only appeared in eight matches (575 minutes overall), scoring six times.

During the 2009–10 season, he was promoted to Linense's first team, but only made four appearances, all from the bench, 89 minutes overall, being later separated from the squad due to indiscipline problems.

[4][5] In January 2010, Walker signed with UD Los Barrios,[6] and made his debut on the 31st, against Puerto Real CF.

[13] In July 2012, Walker was called by Portsmouth manager Michael Appleton to train with the club, after an impressive performance for Gibraltar.

[17] However, due to his international clearance not being made by RFEF in time, he was unable to play on the opening day of the League One season against Bournemouth.

He only made his debut on 21 August 2012, in an away match against Colchester United, coming in for Kieran Djilali who started on the bench.

[23] It was reported that Walker turned up at a training base of Dundee United in Spain without notice and requested a possible trial.

On 9 January 2014, it was announced that Walker had been released from his contract with CD San Roque after his buyout clause had been met.

[31] He played 14 total games during his time in the Middle East, scoring a long-range free kick in a 2–0 win at Hapoel Ra'anana on 1 February.

[46] Walker played in 2011 Island Games, starting in all Gibraltar's matches, and scoring a hat-trick against Ynys Môn on 27 June.

[50] On 6 September 2016, Walker scored his first international goal as Gibraltar made their World Cup qualifying debut against Greece.

Walker hit the net with a curling left-footed shot from just inside the box, levelling the score at 1–1 before his side eventually fell to a 1–4 defeat.

[52] Walker scored his second international goal on 25 March 2018, a deflected free-kick which proved decisive as Gibraltar beat Latvia 1–0 in a friendly, their first win on home soil since joining UEFA.

[54] On 8 September 2024, Walker scored directly from a corner and saw a penalty saved as Gibraltar drew 2–2 with Liechtenstein in the 2024-25 Nations League.