He turned pro in 2001 with HC Thurgau of the Swiss Nationalliga A. Lemm then moved to EHC Kloten where he played through the 2007-08 season. After playing for HC Lugano from 2008 to 2010, he now is back with Kloten. Lemm played for Switzerland in the 2001 and 2002 IIHF World U18 Championships; the 2003 World Junior Ice Hockey Championships; the 2006, 2007, 2008, and 2009 World Championships; and the 2006 and 2010 Olympics.