Petty was taken with pick 37 in the
2017 national draft and appeared in one game in the
2018 AFL season, and spent the rest of the year developing in the
VFL with
Casey Demons. Petty started the
2019 AFL season in defense but was shifted to the forward line for the first time in his career. He kicked three goals in his first game forward, and three more in the next four weeks before injury kept him out of the last two games. After recovering from a groin injury, Petty started the
2021 AFL season in Melbourne's reserves side, before being recalled after a season-ending knee injury to
Adam Tomlinson. After starting the
2023 AFL season in defence, he was used as a forward again, before a foot injury in the round 9 game against Hawthorn cost him several weeks. He went forward again in round 20 and kicked a career best six goals against , before another foot injury the following week ended his season. Petty returned to the forward line early in 2024 but struggled for goals, kicking just nine in 20 games. In early 2025, Petty returned to defence but was soon required in Melbourne's struggling forwad line and ended the season with a career high 20 goals. In round 2 of 2026,
Dockers forward
Patrick Voss came under scrutiny for mocking Petty's
bald spot. Voss was fined a reduced $1000 due to an early plea agreement, and received criticism from AFL legends,
Nick Riewoldt &
Max Gawn. ==Statistics==