Early career Devenny came through the youth system at
Kilmarnock. During the 2021–22 season, he was loaned out to
Broomhill in the
Lowland Football League. He joined
Airdrieonians initially on loan in February 2022 and made the move permanent that summer. Devenny helped Airdrie gain promotion to the
Scottish Championship via the play-offs, and scored his first senior goal in the Scottish League Cup win over
Cowdenbeath. He also scored in the play-off semi-final win against Falkirk and converted a decisive penalty in the shoot-out win for Airdrie in the play-off final in May 2023 against
Hamilton Academical.
Crystal Palace Devenny joined
Premier League club
Crystal Palace in August 2023, to start off in their under-21 development team. He made his Premier League debut on 9 November 2024, starting in Palace's 2–0 home loss against
Fulham. On his second start for the first team on 23 November, Devenny scored his first senior goal for Palace in a 2–2 draw against
Aston Villa. He scored in a 2–0 win over
Doncaster Rovers on 10 February 2025 in the fourth round of Palace's
FA Cup-winning campaign, and was later an unused substitute as Palace won
the final on 17 May. On 10 August 2025, following a 2–2 draw against
Liverpool in the
2025 FA Community Shield, Devenny scored Palace's decisive fifth penalty in the ensuing shootout, winning his second trophy with the club; he had previously come inches away from scoring the game-winning goal in stoppage time. Devenny scored his first European goal on 18 December 2025, in a 2–2 draw against Finnish club
KuPS in the
UEFA Conference League. ==International career==