Giro made his AFL debut for Fremantle in the round 11 of the 2018 AFL season, alongside fellow debutant Scott Jones.[3] On debut he kicked one goal and had 10 disposals as the Dockers lost to the Magpies by 61 points.
Before the start of the 2019 season, Stefan signed a two-year contract extension with Fremantle.[4] Unfortunately for Stefan, his 2019 season ended prematurely after injuring his ACL in Peel Thunder's round 8 clash against Subiaco.[5] Giro was delisted by Fremantle at the end of the 2021 AFL season.[6]
In 2022 he signed with Subiaco in the WAFL. It was in 2022 he played 1 AFL match for West Coast against North Melbourne in round 2 as a covid top up player.