The bond between carbon-fiber-reinforced polymers (CFRPs) and concrete plays a key role in externally bonded CFRP-strengthening technology, but it is susceptible to harsh environments. In the present study, the effects of freeze-thaw cycles (−2°C for 1 h and 3°C for 1 h) in water and 9% relative humidity (RH) on the behavior of the bond between CFRP and concrete were investigated using a single-lap shear test. The freeze-thaw process deteriorated the fracture energy, maximum bond stress, initial stiffness, and load capacity of the CFRP–concrete bond. The effects of water immersion were much more severe than those of exposure to 9% RH. In the case of freeze-thaw cycles under 9% RH conditions, the debonding mode shifted from concrete cohesive failure to adhesive/concrete interfacial debonding. In the case of freeze-thaw cycles with water immersion, the debonding mode (concrete cohesive failure) did not vary owing to the severe degradation in the concrete substrate. A model describing the degradation in the fracture energy of the CFRP–concrete bond as a function of the number of freeze-thaw cycles was developed based on parameter analysis, experimental testing, and the results sourced from literature. An environmental coefficient is proposed to account for the degradation in the CFRP–concrete bond due to freeze-thawing. Using the temperature data and a particular number of freeze-thaw cycles, the service life of the CFRP–concrete bonds in actual applications can be predicted.