Ronnie Theseira was a multi-sport athlete in his youth and his accolades ranged from being a local bantamweight boxing champion to a finalist in bodybuilding and ballroom dancing competitions. His greatest passion, however, was for fencing and he helped introduce the sport to Malaysia in the 1950s, founding the Malayan Amateur Fencing Association at the end of that decade and working as a coach. His sole Olympic appearance came at the 1964 Tokyo Games, where he was eliminated in the first round of the individual competitions for all three weapons. He also competed at the 1970 Commonwealth Games and the 1986 World Championships, but did not reach the podium. He served as President of the national federation from 1981 through 1985 and continued to train athletes into his 90s. By career, he worked as a hospital medical records administrator.