Brown started her sporting career playing basketball. She played for Nunawading Spectres in the Melbourne United Victorian Junior Basketball League (MUVJBL) Under 18 Girls competition, making 19 appearances.[1][2][3]
Brown started playing football only at the age of 14, starting out with her local club Donvale.[4] The next year, she joined Eastern Ranges in the NAB League Girls and played for them for three seasons.[5] In the 2019 season, playing as a tough midfielder, she averaged five tackles per game over 10 games for Eastern Ranges and was then selected for the 2020 AFL Women's (AFLW) academy, a nine month program involving camps and training with the AFLW clubs.[6][7] For the 2020 season, she was also included in Eastern Ranges' leadership group.[8]
A year later, halfway through her latest contract, Brown was traded to Carlton in a four-way trade, with Annie Lee joining Collingwood in exchange.[17]
^Mullan, Alanna (27 January 2021). "AFLW: Three Pies to debut". Collingwood. Telstra. The club's first ever father–daughter pick, Tarni Brown will make her debut in the midfield wearing the number 26 made famous by her Dad, Gavin Brown.
^"27 Recommit to the Pies". Collingwood. Telstra. 16 March 2023. Reigning Club Best and Fairest Jordyn Allen heads up a series of top talent in Imogen Barnett, Tarni Brown, Lauren Butler and Aishling Sheridan who have all penned fresh two-year deals.