He made his AFL debut in the twenty-two point win against Port Adelaide at Etihad Stadium in round 4 of the 2018 season.[4]
On 4 September 2019, Guelfi signed a contract extension with Essendon until the end of the 2021 season.[5]
In 2022, Guelfi enjoyed a career best season establishing himself as a quality pressure forward and culminating with a third placed finish in the club's Best and Fairest. He was also awarded the McCracken Medal as the 'Player's Player'.[6]
Following this, he signed a two-year contract extension that would keep him at the club until the end of 2024.[7]
^The 2020 season was played with 17 home-and-away matches per team (down from 22) and 16-minute quarters with time on (down from 20-minute quarters with time on) due to the impact of the COVID-19 pandemic.