Beginning his karting career in his native Austria in 2000, Grubmüller did not move up into the major international series until 2002, with an appearance at the South Garda Winter Cup.

Grubmüller continued at the ICA Junior level in 2004, combining a karting campaign with appearances in the Formula Renault Monza series.

He moved to MGM Racing to drive one of their Birel karts,[2] finishing eighth in the Andrea Margutti Trophy, and third behind Philipp Eng and Marco Wittmann in the Italian Open Masters.

[4] His father Walter had bought into the Hitech Racing team, and installed his son as one of the drivers alongside Marko Asmer.

He impressed in Macau, finishing as top Hitech driver in eighth beating both Chilton and Roberto Merhi, who joined the team for a one-off drive.

Van der Zande had also moved ahead of Grubmüller in the standings, but with van der Zande returning to the Formula Three Euroseries to compete for Motopark Academy in Barcelona, Grubmüller had the chance to seal the runner-up spot, at the final round at Brands Hatch which was being held on the same weekend.

Towards the end of 2008, Grubmüller tested a Formula Renault 3.5 Series car for the first time with leading British team P1 Motorsport at the Paul Ricard circuit in France.