German professional golfer who plays on the European Tour. Siem was born in Mettmann.
He turned professional in 2000 and joined the European Tour in 2002. His first win on the European Tour came at the 2004 Dunhill Championship. Siem then had to wait eight years before picking up his second win in 2012 at the Alstom Open de France. 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. His best year end ranking on the Order of Merit is 14th in 2012.
In March 2013, Siem won for the third time on the European Tour at the Trophée Hassan II in Morocco. He went wire-to-wire to win by three strokes over David Horsey and Mikko Ilonen. 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 BMW Masters, the first event of the Race to Dubai finals series and his fourth overall on the European Tour. He won in a sudden death playoff over Ross Fisher and Alexander Lévy with a birdie on the first extra hole.