He previously played for the South Sydney Rabbitohs, with whom he won the 2014 NRL Premiership and the Manly-Warringah Sea Eagles.

Walker has played at representative level for City Origin, NRL All Stars, New South Wales and the Prime Minister's XIII.

[7] Walker finished his promising debut year in the NRL with him playing in 16 matches, scoring 8 tries and kicking 1 goal.

On 5 October, 2014 NRL Grand Final, Walker played at centre in South Sydney's 30–6 victory against the Canterbury-Bankstown Bulldogs.

[16] Walker made his international debut against New Zealand at Suncorp Stadium, starting at centre then played at fullback in the 2nd half filling in for Greg Inglis in Australia's 30–12 loss.

[18] On 23 January 2015, Walker was named in the South Sydney Rabbitohs tournament winning 2015 NRL Auckland Nines squad.

In the early hours of 22 September 2015, Walker and fellow South Sydney teammate and best friend Aaron Gray were hospitalized after the pair overdosed on prescription drugs Oxycodone and Tramadol.

At the official announcement of his signing during a Manly pre-season training camp in Coffs Harbour, Walker told the Sydney Morning Herald "Five-eighth was my favourite position coming through the juniors and if the coach (Barrett) wants me there I will jump at the opportunity".

[32] In Round 1 of the 2016 NRL season, he made his club debut for Manly-Warringah against the Canterbury-Bankstown Bulldogs, starting at five-eighth in the Sea Eagles' 28–6 loss at Brookvale Oval.

[34] On 1 June, he made his debut for New South Wales against Queensland in Game 1 of the 2016 State of Origin series, coming off the interchange bench.

On 28 September 2017, Walker broke his leg and fractured his ankle while playing for The Australian Prime Ministers’ XIII side.

[38][39][40] In Round 11, Walker suffered a fractured eye socket after getting into a fist fight with Melbourne player Curtis Scott.

Walker played a total of seven games at five-eighth for Manly-Warringah in the 2020 NRL season as they finished a disappointing 13th on the table.

[46] In Round 1, Walker started the 2021 NRL season at fullback where he played the first 5 games, before reverting back to his preferred position of centre, after Dally M Player of the Year, Tom Trbojevic, returned to the squad from injury.

Walker played a total of 19 games for Manly in the 2022 NRL season as the club finished 11th on the table and missed the finals.

Walker’s veteran experience and his versatility and ability to play multiple positions (prop, hooker, second row, lock, centre, halfback, or five-eighth) helped guide the New Zealand Warriors to their first top 4 ladder finish since 2008.

Due to a calf injury to starting halfback Shaun Johnson before Week 1 of the Finals, Walker was shifted to five-eighth in the New Zealand Warriors’ 32-6 loss to Penrith.

Walker played off the bench and put in a strong performance in the clubs preliminary final loss to the Brisbane Broncos.

On 10 May 2019, at the court hearing, the magistrate dismissed the charges, saying she was not satisfied beyond a reasonable doubt that Walker had assaulted his partner.