Since 1990 to the 2000s, Prahl was one of Sweden's most successful managers, winning three league titles. He debuted in 1992 in Allsvenskan with Trelleborgs FF. He won the league since then with both Malmö FF and Halmstads BK. On January 1, 2006 he took over Viking from Roy Hodgson.  However, his spell with the Stavanger-based club proved unsuccessful, and he was fired in September 2006 on the back of seven losses in eight league matches, with the team on the bottom of the Norwegian Premier League table. Prahl returned to Trelleborg and managed the club until his retirement in 2011.