The Mesoarchean era is marked by rapid growth and compositional transition of continental crust. Most studies have shown that felsic plutons became the main component of the upper crust by around 3.0 Ga, although processes related to the generation of the felsic magma remain debated. In particular, the depth of such felsic melt generation is unclear, mainly due to the lack of pressure-sensitive minerals in felsic plutons. However, garnet, stable at great depths and relatively high temperatures, may hold such information. In this study, Mesoarchean garnet-bearing granites in the Yangtze Craton of South China are investigated. Zircon U-Pb dating results confirm that the host rocks (slightly peraluminous potassic granites) of the garnets were crystallized at 3.0–2.9 Ga. Zircon εHf(t) values range from -7.4 to -3.7, indicating that the host rocks contain reworked old crustal materials. The garnets are pink in colour and mostly euhedral. In BSE images, garnets are homogeneous without zoning, which is also confirmed by major element results, implying that they crystallized from magmas rather than from metamorphic reactions. Nonetheless, a few large garnet crystals show a core-rim structure with very thin rims, with the latter being sometimes altered by post-magmatic fluids. In addition, almandine and spessartine are the main components of the garnets, which are consistent with the typical compositions of magmatic garnets. Only quartz is found in garnet inclusions, and some garnets occur as inclusions in plagioclase, which argue against a peritectic origin. Different from the major elemental features in individual garnet grains, profiles of HREEs (Lu and Yb) in many grains show a systematic decrease from cores to rims, which may be caused by continuous growth of garnets. Zr/Hf ratios and Eu/Eu* values in all garnets show a positive correlation, as is observed in zircon, demonstrating that fractional crystallization of zircon and plagioclase occurred during magma evolution. Because high pressure (> 0.9 GPa) is generally required to reach the stability field of garnet, the occurrence of Mesoarchean garnet-bearing granites suggests the presence of a mature thick continental crust at ca. 2.9 Ga.