During the 1960s Hans Rosendahl was one of the best freestyle swimmers in Sweden. Rosendahl had his first international success with gold in the 4 × 200 metres freestyle relay at the 1962 European Aquatics Championships in Leipzig along with compatriots Per-Ola Lindberg, Mats Svensson, and Lars-Erik Bengtsson. Rosendahl also won an individual silver in Leipzig when he finished second in the 400 metres freestyle. Two years later he was part of Swedish quartet that came fifth in the 4 x 200 metres freestyle relay at the 1964 Tokyo Olympics, along with him finishing tenth in the 400 metres freestyle. After his swimming career Rosendahl played water polo at an elite level and later become a PE teacher.