Rubuta ci gaba don wannan sakin layi - Wani ɗalibin shari'a, ya fara aikin soja a lokacin da yake da shekaru goma sha takwas, bayan da aka kafa junta a 1810, wanda ya fara aiwatar da 'yancin kai a New Granada. Santander ya shiga cikin sojojin juyin juya hali a watan Oktoba na 1810, a cikin rundunar soja na National Guard ("Guardias Nacionales"). Da farko ya yi aiki a matsayin soja a rundunar sojojin Tarayyar Tarayyar Tarayyar New Granada, a karkashin jagorancin Janar Antonio Baraya, wanda ya yi yaƙi da Janar Antonio Nariño, na lardin Cundinamarca, wanda ya ƙi amincewa da ikon Tarayyar. A lokacin waɗannan kamfen ɗin Santander ya sami mukamin Kanar a 1812. Bayan sojojin sarauta sun sake cinye New Granada
, Santander kamar sauran jami'an New Granada da yawa sun koma filayen gabashin Cordillera Oriental, Llanos, kusa da iyakar Venezuela ta zamani. A can, Santander ya haɗu da sojojin Venezuela masu kishin ƙasa kuma ya yi aiki a ƙarƙashin umurnin Simón Bolívar. A lokacin yakin soja a fadin Andes, Bolívar ya inganta Santander zuwa Brigadier Janar a 1817.