Al–Mg–Li alloy was prepared using powder metallurgy and hot extrusion methods. The microstructure, fracture morphology and mechanical properties of the alloy were analyzed using metallographic microscopy, scanning electron microscopy, transmission electron microscopy, and a tensile testing machine. The effects of different Mg/Li ratios (1.3, 1.8, 2.5) on the microstructure and mechanical properties of the alloy in the sintered, extruded, and T6 heat-treated states were investigated. The results revealed that an increase in the Mg/Li ratio led to an increase in the relative density of the sintered alloy, indicating the promoting effect of Mg on the sintering process. For the extruded Al–Mg–Li alloy, as the Mg/Li ratio increased, the precipitation of Mg-containing phases gradually increased and clustered near the grain boundaries, resulting in improved mechanical properties, the tensile strength of which increased from 285 MPa to 407 MPa. After T6 heat treatment, the second phase in the Al–Mg–Li alloy mainly consisted of δ′ phase and T phase. The δ′ phase, as the main strengthening phase, was uniformly distributed in the aluminum matrix, while the T phase exhibited a chain-like distribution along the grain boundaries. Increasing the Mg/Li ratio enhanced the tensile strength and yield strength of the alloy, but it may lead to a decrease in elongation. For instance, the Al–5Mg–2Li alloy after T6 heat treatment exhibited a tensile strength of 532 MPa, a yield strength of 473 MPa, and an elongation of 4.5%.