Club Guaraní is the second oldest Paraguayan football club. It was founded in 1903 under the name of "Football Club Guaraní" and its first president was Juan Patri. The name of the club derives from the Guaraní people, a big part of Paraguayan culture and history. The colours of the club, black and yellow, were proposed by the Melina brothers (also among the founders of the club) in reference to the colours of Uruguayan club Peñarol, where the Melina brothers played for a few years. The mentioned colors were also used by English privateerFrancis Drake in his emblem and shield, which is another reason why they were chosen to represent the club.
Guaraní is one of the traditional teams from the Paraguayan football league and during their history they have won a total of ten championships and were runners-up in fourteen occasions. The most successful era in their history was in the 1960s, where they had an excellent team that won three titles. This era is known as the "golden decade" by the Guaraní fans.
Along with Olimpia, they play the "clásico añejo" (the oldest derby) because they are the two oldest teams from Paraguay. Also, Guaraní, Cerro Porteño and Olimpia are the only teams that have never played in the second division of the Paraguayan league.
In late May 2010, Guaraní became champions after 26 years after defeating Olimpia in a match that ended 2–1 to clinch the 2010 Apertura title.