Jos Rosa partnered with Charles Van Antwerpen to represent Belgium in the coxless pairs at the 1948 London Olympics, where they were eliminated in the round one repêchage. They had more success at the next two editions of the European Championships, taking silver in that event in 1949 and bronze in 1950. In 1951 they joined a coxless fours crew that included Harry Elzendoorn and Florent Caers and together they captured the European Championship title in that event. This led to their selection for the 1952 Helsinki Olympics, but the Belgian squad was eliminated in the semifinals. Rosa retired from active competition shortly thereafter.