Walker was born in Toowoomba in Southern Queensland on 13 September 1976, and is the eldest of a trio of brothers who would all become rugby league footballers. While attending St Mary's Christian Brothers College in Toowoomba in 1993, Walker was selected in the Australian Schoolboys team.[3]
Playing for the Northern Eagles in the 2001 National Rugby League season, Walker was the equal competition leading point scorer (along with Newcastle's Andrew Johns) with 279 points (17 tries, 102 goals, 1 field goal) in 26 games,[4] receiving the Dally M Award for Top Points Scorer. Walker had kicked 102 of his 125 shots on goal, a percentage of 82.40 for the season. This stands as the most ever points scored by a five-eighth in a single National Rugby League season. Walker's 279 points is also the most points ever scored for the short lived Northern Eagles (2000–02) and the most points in a season by an Eagles player. Even though he only played for the Eagles in 2001, Walker's 279 points for the season remains the club record (The Northern Eagles played from 2000 to 2002). The next highest scorer for the club is Brendon Reeves who scored 130 points (30 tries, 5/10 goals) in 66 games from 2000 to 2002.
Walker was the first player in the NRL to score during golden point (extra-time). He kicked a penalty goal for Manly against Parramatta at Brookvale Oval on 18 May 2003.[5]