Büchner joined Millward Brown Germany in 2007 as deputy managing director.
Before joining the consultancy, which has German offices in Frankfurt and Hamburg, Büchner was a senior market research consultant at TNS Emnid and TNS Infratest in Bielefeld and Munich.
Previous to this he was the managing director of market research firm Report International in Brussels.
Büchner said: "I am very pleased to have been appointed managing director of Millward Brown Germany.
"The company has been very successful in recent years and I am confident that we will grow further in the future.
"In particular, we want to expand our leading position in communications and brand research."