Madarassy competed for Hungary in the men's 100 m butterfly at the 2008 Summer Olympics in Beijing. Leading up to the Games, he registered a time of 54.28 to eclipse the FINA B-cut (54.70) by 0.42 of a second at the USA Swimming Grand Prix in Columbus, Ohio. Madarassy threw down his lifetime best of 53.93 to hit the wall with a fourth-place finish in heat three, trailing winner Rimvydas Šalčius of Lithuania by just more than a second. Madarassy failed to advance into the semifinals, as he placed fiftieth out of 66 swimmers in the prelims.