Marson made his first Paralympic appearance, representing Italy, in the second ever Games in Tokyo, Japan, in 1964. He competed in three different sports: athletics, wheelchair fencing and swimming. In athletics he won two gold medals and two silver medals, setting a new world record of 24.20 metres in the men's javelin C classification. He finished fourth in both of the freestyle swimming events in which he competed. In the individual fencing events Marson won silver in épée and sabre, but alongside compatriots Franco Rossi and Rengo Rogo he won a team épée gold medal and a team sabre bronze medal.