This study investigates the enhanced structural, and optoelectronic properties of transparent conductive Ga-doped MgxZn1−xO (GMZO) thin films with a varied magnesium (Mg) composition of 2% and 8%, respectively. The X-ray diffraction (XRD) measurements revealed that GMZO with an 8% Mg composition shows a stronger (002) diffraction intensity and narrower linewidth than that with a 2% Mg composition. Improved crystallinity and enlarged grain size in the postgrowth thermal annealed GMZO thin films were also observed in XRD and morphological measurements by atomic force microscopy. Photoluminescence measurements were conducted to investigate the improved GMZO thin-film quality, and the oxygen vacancy signal was found to decrease with increased Mg content, consistent with X-ray photoelectron spectroscopy measurements. This study also shows high optical transmittance over 98%, and a low resistivity of 5.7 × 10−4 Ω·cm in Ga-doped MgxZn1−xO (x = 0.02) thin film, which indicates the highly promising candidate for use in optoelectronic devices.