Prahl, born in Eutin, grew up in nearby Neustadt in Holstein. After his A-levels, Prahl started studying music and mathematics, but then went on to acting school in Kiel. His acting debut came in 1994 in a television series for ZDF.
Aside from his film acting, for which he has won several accolades including two Adolf Grimme Awards, Prahl has starred in 23 episodes of the German television crime series Tatort. Prhal also co-starred in the 2009 German TV file 12 Winter with Jürgen Vogel.