Born in Munich, Stiller started his football career at TSV Milbertshofen before joining Bayern youth academy in 2010. Despite his potential, Stiller struggled to secure a place in the first-team squad and eventually moved to Hoffenheim in 2021.
His spell there lasted only two years, but it was at VfB Stuttgart where Stiller truly found his footing. The 23-year-old became a central figure in midfield, amassing nearly 3,000 minutes of game time across 36 appearances in all competitions during the 2023/24 season while contributing one goal and six assists.