Born in Hanover, Prussia, on 11 September 1901, after school education Mühlenfeld studied law and political science at the University of Göttingen where he was granted his doctor of law.

After the war in 1945, Mühlenfeld was a co-founder and from 1950 deputy chairman of the German Party (DP).

[1] Mühlenfeld resigned from the Bundestag on 15 May 1953 in order to take up an appointment as Ambassador of the Federal Republic of Germany in the Netherlands.

This office he held until 1958, when he was appointed to succeed Walther Hess as Ambassador to Australia, where he served until 1962.

From 1963 to 1965 he served in the state SDP-FDP government of Georg Diederichs as Minister of Culture.