Guillermo Douglas began his sports career in 1924 at the rowing club in his hometown of Paysandú. In 1925, only 15-years-old, he took part in the endurance regatta Colón-Paysandú. After that he took up competitive rowing and trained in the capital, Montevideo. In 1931 Douglas won the single sculls at the first South American Rowing Championship in the Bay of Montevideo. Douglas was the first Olympic medal winner from Uruguay in an individual competition. Previously, only the football team had won gold medals in 1924 and 1928. In recognition of his third place, the Montevideo Rowing Club awarded him a scroll and gold medal. He was again successful in 1935 at the 2nd South American Championships in Rio de Janeiro, winning a silver medal. In addition he was a multiple national champion and won numerous competitions in the waters of the Tigre, Lujan and La Plata rivers in Argentina. In 1997 the Uruguayan post office issued a stamp commemorating his achievement.