 Brüner was born in Bad Nauheim in Hesse and began his working life as an apprentice businessman in Darmstadt in 1968.Three years later he went to the University of Munich to study law, economics and political science, and in 1976 joined the Ministry of Justice in Bavaria to train for the judiciary.In 1979 he became an investigating and trial judge in criminal matters at the Municipal Court Weilheim in Oberbayern.