He made his screen debut in 2005 in two commercials directed by Caroline Link. He gained wider recognition through his role as Nerv in the successful film series "The Wild Soccer Bunch" (parts 3-5). In the remake of Max von der Grün's young adult novel "The Crocodiles," Reimann played Hannes, as he did in the two sequels, "The Crocodiles 2" (2010) and "The Crocodiles 3" (2011).

In 2009, he began recording the audiobooks of Jeff Kinney's "Diary of a Wimpy Kid" series and has since been the German voice of Greg, whom he also dubbed in the 2010 American film adaptation, "Diary of a Wimpy Kid: The Movie." Also in 2010, he lent his voice to the role of Sosuke in Hayao Miyazaki's animated film "Ponyo."