He turned professional in 2000 and joined the European Tour in 2002. This victory ensured Siem"s place in the 2012 Open Championship and his first appearance in a World Golf Championship at the WGC-Bridgestone Invitational. Marcel finished the tournament 51st in the world, just missing out on an invitation to his first Masters.
In November 2014, Siem claimed victory at the Bayerische Motoren Werke Masters, the first event of the Race to Dubai finals series and his fourth overall on the European Tour.
Siem represented Germany at the World Cup in 2003, 2004, and 2006. In 2006 he was Bernhard Langer"s team-mate in the second winning German team in the World Cup.
1999 Spanish Amateur Championship, Sherry Cup (Spain) European Tour wins (4) Other wins (1) DNP = did not play CUT = missed the half-way cut "T" = tied Yellow background for top-10. Summary Most consecutive cuts made – 2 (twice) Longest streak of top-10s – 0 Amateur Eisenhower Trophy (representing Germany): 1998, 2000 Professional World Cup (representing Germany): 2003, 2004, 2006 (winners), 2013 Royal Trophy (representing Europe): 2012.