After buying, modifying and selling a Formula Vee chassis of his own, Gartner began his motor sport career in some hillclimbing events in 1976.

He was subsequently invited to take Höttinger's place in the BMW M1 Procar Championship series, in which he raced against Formula One drivers, driving for fellow Austrian Helmut Marko.

After a fourth place at Hockenheim, he won the Pau Grand Prix when the first driver across the line, Alain Ferté, was disqualified because his car was underweight.

In 1984, Gartner had secured the part-time second seat with the struggling Italian Osella team, as teammate to Piercarlo Ghinzani, driving a year-old, non-turbo FA1E.

At the 1984 British Grand Prix, Gartner was allowed to start in 27th position because the Tyrrell Racing team was participating under appeal.

[5] After mechanical failures in the next two races, he finished 12th at the Dutch Grand Prix, five laps down on the winner Alain Prost.

However, Gartner was denied the two points normally awarded to the fifth-place finisher, as Osella had only entered one car at the beginning of the season.

[3] Gartner had finished fourth in the 1985 24 Hours of Le Mans in a Porsche 962C along with teammates David Hobbs and Guy Edwards.