Grain-scale twinning and detwinning in extruded Mg-2.4wt.%Nd was characterized using combined far-field and near-field High Energy X-Ray Diffraction Microscopy (HEDM) during fully reversed tension-compression cyclic straining. Nucleation of {101 ̅2} twins were identified by tracking the appearance or disappearance of {0002} diffraction peaks for all possible twin variants of each grain in the unloaded state. The evolution of twin volume fraction was measured by combining a near-field HEDM reconstructed 3D grain morphology and far-field HEDM spot integrated intensity during cyclic loading. The mechanical response and twin activity in the near-field HEDM reconstructed volume were simulated using a crystal plasticity finite element model with an advanced twinning-detwinning algorithm to characterize the impact of binary Nd alloying on critical resolved shear stresses for the operative slip modes and extension twinning. Twinning is observed during loading parallel to the extrusion axis in both tension and compression due to the weak rotated basal extrusion texture, with a higher total twin volume fraction and number of active variants observed during tensile loading. Twin activity is detected predominantly in large grains, and grains nominally oriented favorably for extension twinning and unfavorably for prismatic slip. Twin growth is observed to lead to elastic strain shielding in the parent lattice during continued macroscopic deformation, and elastic strain accommodated by twin growth is preferentially shifted to pyramidal II <c+a> slip systems during reversed displacement.