After touring cars he joined to Ferrari AF Corse with Toni Vilander and won the FIA GT Championship in GT2 class.

In 2009, Müller rejoined BMW to spearhead its factory program with Rahal Letterman Racing in the American Le Mans Series.

He and Joey Hand won the 2011 American Le Mans Series GT driver's championship following wins at the Twelve Hours of Sebring, Grand Prix of Long Beach and Lime Rock Park.

Müller was entered as an international driver in the 2011 Armor All Gold Coast 600 for V8 Supercars, alongside second-generation racer Steven Johnson.

He was reunited with teammate Joey Hand, while Sébastien Bourdais joined the team for the endurance races including Le Mans.