2015–2022: Early years Karl joined the academy of
Viktoria Aschaffenburg in 2015, and he moved to the academy of
Eintracht Frankfurt in 2017. In June 2018, at 10 years of age, Karl took part at a scouting tournament in Aschaffenburg, progressing to the next round and being invited to audition in the
Bernabéu by
Real Madrid. However, his family prevented a move as they felt that it wasn't really about their son at all – but rather about negotiating contracts for large
football agencies. In 2022, Frankfurt wanted to extend Karl's academy contract, but since
Bayern Munich showed strong interest, Karl expressed his willingness to join Bayern's academy in the summer, which led to his exemption at Frankfurt at the beginning of the year. Bridging his time until summer, he immediately rejoined Viktoria Aschaffenburg for the remainder of the season, before he joined Bayern Munich's
academy.
2022–2025: Bayern academy During the 2024–25 season he started with the
U17 Nachwuchsliga Group F for Bayern Munich with 17 goals and 8 assists in just 9 appearances. At only 16 years of age, Karl already represented both the
under-17 and
under-19 squads during the
2024–25 season, featuring at the
UEFA Youth League.
2025: First team debut On 4 April 2025, he received his first call-up to the senior team of
Bayern Munich, for a 3–1 away victory
Bundesliga match against
FC Augsburg, as an unused substitute and would also feature in Bayern Munich's
Champions League quarter-final squads against
Inter Milan. Two months later, on 15 June, Karl made his professional debut during a 10–0 victory over
Auckland City in the
FIFA Club World Cup, playing the full second half. With Bayern, he would reach the quarter-final, being knocked out by
PSG.
2025–26: Breakthrough season Karl was one of the players that were called up by Bayern Munich head coach
Vincent Kompany, for the
2025 pre-season matches against
Ligue 1 club
Lyon,
Premier League club
Tottenham Hotspur, and
Swiss Super League club
Grasshopper. Against the latter two he'd score his first two senior goals. On 8 August, Karl extended his contract with the club and chose to wear the shirt number 42, which was previously worn by
Jamal Musiala, after having worn 46 in the previous months. Later that year, on 22 October, he scored his first professional goal in a 4–0 victory over
Belgian Pro League club
Club Brugge in the
Champions League, becoming the club's youngest-ever scorer in the competition at 17 years and 242 days old, surpassing the previous record held by Jamal Musiala. Three days later, he netted his first Bundesliga goal in a 3–0 away win over
Borussia Mönchengladbach. On 22 November, he recorded a goal and an assist in a 6–2 victory over
SC Freiburg, becoming the youngest Bayern Munich player to achieve this feat in a single Bundesliga match. Four days later, he'd become the first player in the 2025–26 Champions League season to score a goal against
Arsenal. On 9 December, he netted a goal in a 3–1 victory over Portuguese
Primeira Liga club
Sporting CP, becoming the youngest player ever to score in three consecutive Champions League matches, breaking the previous record set by
Kylian Mbappé. On 18 March 2026, Karl scored his fourth Champions League goal in the round of 16 second leg, a 4–1 home victory over
Atalanta. On 4 April 2026, Karl scored a late extra-time winner in the 98th minute against
SC Freiburg and assisted a previous goal, to help Bayern go 9 points clear of
Dortmund in the
Bundesliga title race, scoring his 5th league goal of the season. On 10 April, Karl suffered a
torn muscle fibre, being sidelined for at least 3 weeks, missing Bayern's 4–3 win (6–4 on aggregate) over
Real Madrid in the quarter-final of the Champions League. ==International career==