Smarsch joined Hertha on 27 September 2017.[1] He made his professional debut on 24 November 2019, when he came on as a substitute after the dismissal of Rune Jarstein in the 28th minute of Hertha's 4–0 defeat at FC Augsburg; they were 2–0 down at the time he came on.[2]
On 2 August 2020, Smarsch joined 2. Bundesliga side FC St. Pauli on a free transfer. He signed a three-year contract.[3] After three years, he left St. Pauli in July 2023 to join MSV Duisburg.[4] After one year, he left Duisburg to join Hertha BSC for the 2024–25 season.[5]