Rapid developments in wide-bandgap semiconductors have led to the demand for interconnection materials that can withstand harsh conditions. In this study, novel Ag composite pastes were developed with the assistance of metal organic decomposition (MOD) to significantly reduce the sintering temperature of commercial Ag pastes. The effects of the decomposition characteristics of different MODs on the microstructure, morphology, and the shear strength of the Ag-sintered joints were systematically investigated. Additionally, the low-temperature sintering mechanisms of the MOD-assisted Ag composite pastes were studied and proposed. Among all the MODs studied, the one consisting of propylamine complexed with silver oxalate demonstrated the best performance due to its ability to form Ag nanoclusters with the smallest size (~25 nm) and highest purity (~99.07 wt.%). Notably, the bonding temperature of the MOD-modified Ag pastes decreased from 250 °C to 175 °C, while the shear strength increased from 20 MPa to 40.6 MPa when compared to the commercial Ag pastes.