Externally bonded glass and carbon fiber reinforced polymer composites are increasingly being used to upgrade, repair, and rehabilitate steel reinforced concrete structures such as beams and slabs. The effectiveness of the bonded composites depends on the integrity of the composite/concrete bond over years of exposure to sustained loads and various weather conditions. The present investigation was conceived with the aim of characterizing bond behavior over a long period of time in realistic indoor and outdoor environments, with sustained loading. Plain concrete beams were externally reinforced with wet-layup glass and carbon composites and subjected to sustained flexural loads for 6 years. Then, the beams were loaded to failure while strains on the composite were recorded using resistance strain gages and full-field digital image correlation. The results indicate that ultimate bond strength is strongly correlated with changes in the concrete strength. This finding is consistent with bond failures being mainly controlled by the concrete rather than the composite material. Glass composite specimens generally had less debonding prior to failure, along with higher strength concrete. Furthermore, it appears that the sustained loading itself had little effect on the ultimate bond strength.