Brandl qualified for the men's 400 m freestyle at the 2008 Summer Olympics in Beijing, by attaining a B-standard entry time of 3:51.35 from the Austrian Swimming Championships, coincidentally in his home city Linz. He won the second heat by twenty-one hundredths of a second (0.21) ahead of France's Sébastien Rouault, with an Austrian record-breaking time of 3:48.63. Brandl, however, failed to advance into the final, as he placed twentieth out of 37 swimmers in the evening preliminaries. Three days later, Brandl swam on the second leg of the men's 4 × 200 m freestyle relay, recording his fastest individual-split time of 1:46.45. Brandl and his teammates Markus Rogan, Dominik Koll, and Florian Janistyn finished heat two in fifth place and ninth overall, for another Austrian record time of 7:11.45.