In April 2016, Bouhaddouz agreed to a three-year contract with FC St. Pauli. In his first season there, he amassed 15 goals and 6 assists in the league. Over two seasons at the club he scored 19 goals while assisting 8 in 54 league appearances.
Bouhadddouz was born in Morocco, but raised in Germany and was eligible for both national teams. He made his debut for the senior Morocco national football team in a friendly 0–0 tie with Albania in August 2016. A month later, he scored his first goal for his country, netting in a 2017 Africa Cup of Nations qualification match against São Tomé and Príncipe.