Born in Asunción, Dos Santos started his professional career with Cerro Porteño, before eventually moving to FC Bayern Munich of Germany, in January 2006. He was elected Paraguayan Footballer of the Year in 2005 by national newspaperDiario ABC Color. Upon his arrival in Munich, he was touted as a long-term successor to Michael Ballack, but faced stiff competition from Iran's Ali Karimi. Eventually, both players struggled to break into the starting lineup. In the first half of 2006–07 Bundesliga season, Bayern's leadership publicly stated its impatience with Dos Santos' progress. Club coach Felix Magath said: "It is clear that Julio's development does not please us, It does not make sense to keep a player at the club who does not create". This led to widespread rumours of his departure from the club; the speculation ended in December 2006, when Bayern announced they had reached a deal to send the player on loan to fellow Bundesliga side VfL Wolfsburg for the remainder of the season. Having failed to break into Wolfsburg's first team, he returned to Bayern in June. At the conclusion of the 2006–07 season, Dos Santos had made four league appearances, as well as one appearance in the 2006–07 DFB-Pokal and two appearances in the 2006–07 UEFA Champions League. However, after the arrivals of Franck Ribéry, Hamit Altıntop, José Sosa and Zé Roberto, it soon became clear that he would again struggle to find a place in the first team. Ottmar Hitzfeld, who had replaced Magath as Bayern manager by that time, stated that the club sought to sell dos Santos. Therefore, he would split 2007–08 between UD Almería and Grêmio Foot-Ball Porto Alegrense. In June 2008, dos Santos signed with Clube Atlético Paranaense, also from Brazil. In June 2009, Julio went back to his original club Cerro Porteño to play the 2009 Clausura and Copa Sudamericana. On 29 December 2014, Julio dos Santos joined Brazilian club Vasco da Gama. Before signing with Sportivo Luqueño, dos Santos rejected the opportunity to sign with Olimpia Asunción – being Cerro Porteño's rival – thanking however the club's president for interest in him but stating that his Cerro-ism would not permit him to join Olimpia.
