The effect of initial texture on slip activity, dynamic recrystallization, and basal texture development was investigated in a Mg–9 wt.% Ag alloy during high-temperature plane strain compression. Three sets of specimens with different initial compression planes were machined from a hot-rolled plate and compressed at 723 K and a strain rate of 5.0 × 10⁻² s⁻¹ up to a true strain of −1.0. Microstructure and texture analyses revealed that the initial texture strongly affected the subsequent texture evolution and microstructural development. Sample A, which initially exhibited a strong basal texture, retained and intensified the basal component during deformation, whereas Sample B maintained a transverse direction texture component and showed the lowest flow stress, the highest kernel average misorientation, the lowest dynamically recrystallized fraction, and the retention of coarse unrecrystallized grains. These features suggest that prismatic slip was geometrically favored at the early stage of deformation, resulting in enhanced intragranular deformation and delayed rotation toward the stable basal texture. In contrast, Sample C initially exhibited a rolling direction texture component but rapidly evolved toward a strong basal texture, particularly between true strains of −0.7 and −1.0. Although dynamic recrystallization contributed to grain refinement and local orientation scattering, the final texture evolution was governed mainly by slip induced lattice rotation rather than recrystallization induced texture randomization. These results demonstrate that, although Ag addition can modify flow and recrystallization behavior, basal texture development remains dominant when slip-induced lattice rotation is strongly favored by the imposed plane strain compression geometry.