Florian Grillitsch was born on 07/08/1995 in Neunkirchen, Austria. He played for SVSF Pottschach and St. Pölten in his youth football career. Grillitsch joined Werder Bremen on 1 July 2013. He split the 2013–14 season between the Werder Bremen U19's youth team and Werder Bremen II. He made 15 appearances in the A-Junioren-Bundesliga Nord/Nordost, scoring 11 goals. Grillitsch made his first team debut during the 2015–16 season. On 16 January 2017, he signed a contract with 1899 Hoffenheim until 2021, starting from the 2017–18 season.