When exposed to moderate to high temperatures, nanomaterials typically suffer from severe grain coarsening, which has long been a major concern that prevents their wider applications. Here, we proposed an effective strategy to inhibit grain coarsening by constructing grain boundary (GB) complexions with multiple codoped dopants, which hindered coarsening from both energetic and kinetic perspectives. To demonstrate the feasibility of this strategy, multiple selected dopants were doped into a ZrO₂–SiO₂ nanocrystalline glass ceramic (NCGC) to form GB complexions. The results showed that NCGC was predominantly composed of ZrO₂ nanocrystallites (NCs) distributed in an amorphous SiO₂ matrix. Ultrathin layers of GB complexions (~2.5 nm) were formed between adjacent ZrO₂ NCs, and they were crystalline superstructures with co-segregated dopants. In addition, a small amount of quartz solid solution was formed, and it adhered to the periphery of ZrO₂ NCs and bridged the adjacent NCs, acting as a “bridging phase”. The GB complexions and the “bridging phase” synergistically enhanced the coarsening resistance of ZrO₂ NCs up to 1000 °C. These findings are important for understanding GB complexions and are expected to provide new insights into the design of nanomaterials with excellent thermodynamic stability.