Guallatiri volcano is an active stratovolcano located in the Arica y Parinacota Region of northern Chile. It belongs to the Central Volcanic Zone (CVZ) of the Andean range and is the youngest and southernmost volcano of the Nevados de Quimsachata volcanic chain. Guallatiri is an ice-capped volcano considered the third-highest risk center in northern Chile with a current activity characterized by two fumarolic fields with strong and persistent gas emissions. This work presents the first detailed geological mapping of the volcano based on stratigraphic, petrographic, morphological, and geochemical data. The volcano has evolved into seven units, whit the initial stages characterized by the widespread and effusive emission of several thick lava flows around the volcanic edifice. The later evolution units involved the extrusion of lava domes at the summit, with a Holocene plinian eruption accompanied by pyroclastic density currents, tephra fallout, and lahars. Furthermore, two parasitic Holocene domes, Tinto and South domes were nested on the volcano’s southwestern flank. High eruptive rates (0.36 km3/ka) indicate that Guallatiri volcano has been one of the most active volcanoes during the Late Pleistocene-Holocene. The volcanic products from Guallatiri mainly correspond to trachyandesites, trachydacites, and dacites rich in amphibole and biotite, with minor clinopyroxene and olivine. They belong to the High K2O Calc-Alkaline Series, similar to other active volcanoes of the region. The construction of detailed geological maps of active volcanoes is used as the basis for the generation of hazard and risk maps, which enable the mitigation of associated volcanic risks. In the case of Guallatiri, the occurrence of lahars, pyroclastic flows, and tephra fallout are considered the main volcanic hazards, which could affect the villages of Guallatire and Ancuta, in addition to small hamlets in Bolivia.