After graduating from school in Ingolstadt, Müller finished an apprenticeship as a toolmaker at Audi in 1977. He then studied computer science in Munich, returning to Audi and taking a junior managers position in the IT department in 1984. After joining the planning department from 1993 Müller was product manager for the Audi A3, and from 1995 he was given overall responsibility for product management at Audi.
A year after Martin Winterkorn took over management at Audi, in 2002 Müller was appointed coordinator of Audi and Lamborghini model lines. After Winterkorn was appointed VW Group boss in 2007, he appointed Müller as general representative, and then head of VW's product strategy, controlling all VW group brands.