Wire Arc Additive Manufacturing (WAAM) is a cost-effective method for fabricating large aluminum components; however, it tends to suffer from heat accumulation and coarse anisotropic microstructures, which can limit the part's performance and its mechanical properties. In this study, a wall is fabricated using a hybrid unified additive deformation manufacturing process (UAMFSP) method, which integrates friction stir processing (FSP) into WAAM, and is compared with a WAAM-only wall fabricated by Metal Inert Gas (MIG) deposition. Based on the outcomes, Infrared (IR) thermography revealed progressive heat buildup in WAAM-only MIG walls, with peak layer temperatures of about 870 to 1000 °C and occasional clipped peaks near the IR-camera limit (~1300 °C). In contrast, in the UAMFSP process, heat was redistributed through mechanical stirring, maintaining more uniform sub-solidus profiles below approximately 400 °C. Also, optical microscopy and quantitative image analysis showed that MIG walls developed coarse, dendritic grains with a mean grain area of about 314 µm², whereas the UAMFSP produced refined, equiaxed grains with a mean grain area of about 10.9 µm², which is approximately 1.5 orders of magnitude smaller. Mechanical performance assessment through microhardness measurement confirmed that the UAMFSP process can improve the hardness by 45.8% compared to the MIG process (75.8 ± 7.7 HV vs. 52.0 ± 1.3 HV; p = 0.0027). In summary, the outcomes of this study introduce the UAMFSP process as a robust method for addressing the thermal and microstructural limitations of WAAM and improving the performance of the fabricated part. By combining deposition with plastic deformation, UAMFSP enables the fabrication of aluminum parts with fine isotropic microstructures and improved strength. These findings provide a framework for further extending hybrid additive-deformation strategies to thicker builds, alternative alloys, and service-relevant mechanical evaluations.