For almost two decades Ioannis Thymaras was the goalkeeper for the Ethnikos Piraeus water polo club, which saw them dominating the sport in Greece. With the club Thymaras won 14 consecutive Greek Championships from 1957 to 1970, along with two Greek Cups in 1957 and 1958. During this time the team only lost two championship matches, one in 1964 and the second in 1968. He also made 50 appearances for the Greek national team, including playing in all eight of their matches at the 1968 Mexico City Olympics. Following his playing career Thymaras went on to coach Ethnikos Piraeus, where he won a further four Greek Championships (1974–77).