[2] Walker made his debut for the St Patrick's Athletic first team on 8 August 2017 when he came off the bench for Josh O'Hanlon for the last 2 minutes of a 2–1 Leinster Senior Cup win over Firhouse Clover at Richmond Park.
[3][4] He did not feature in the 2018 season with forward options including Christy Fagan, Jake Keegan and Achille Campion at the dispense of manager Liam Buckley.
His next involvement with the first team came on 18 February 2019 when he came off the bench for the injured Gary Shaw in a 3–0 Leinster Senior Cup win over Wexford, with Walker heading home a James Doona cross after 58 minutes to put his side 2 goals in front.
[8] Walker made 10 more substitute appearances in a row before coming off the bench and scoring the winner against Finn Harps on 14 June with 7 minutes to go, the first league goal of his senior career.
[19] On 22 October 2019 Walker came off the bench away to Derry City in the 69th minute with the scores level and brilliantly set up two goals for fellow substitute James Doona to secure a 3–1 win for the Saints at the Ryan McBride Brandywell Stadium.