Developing full-spectrum photocatalysts that harvests solar light from ultraviolet to near-infrared light has aroused great interest in photodegradation of organic pollutants, due to the imminent energy crisis and growing pollution issues. Herein, we report an excellent full-spectrum photocatalyst derived from calcination of an Mg/Zn/Al/Er-hydrotalcite-like compound. The photocatalyst is a stable multi-phase oxide consisting of various syntrophic Er³⁺-doped metal oxides with different particle sizes and morphology. Its ultraviolet (UV) photocatalytic activity is maximized by increasing the fraction of Zn²⁺ and sustaining the pure hydrotalcite-like phase with an appropriate fraction of Mg²⁺ in preparing the Mg/Zn/Al/Er-hydrotalcite-like precursor. The visible and NIR photocatalytic activities are triggered by an indirect excitation involving an up-conversion process. The major active species of the photocatalyst in the photodegradation of methyl orange are superoxide anions and photogenerated holes. Nevertheless, hydroxyl radicals also play a moderate role in the photodegradation process. This work finds a new way to prepare full-spectrum photocatalysts with tunable chemical compositions via an environmentally friendly hydrotalcite-like precursor.