This work investigates the Mode I delamination behavior of adhesive joints made on a unidirectional carbon fiber-reinforced epoxy composite (CFRP), under both static and fatigue loading. The specimens were subjected to two controlled degradation environments: hygrothermal conditions in a climatic chamber (60 ℃ and 70% RH) and a saline environment (35 ± 2 ℃, 89% RH, 1.2 bar, NaCl “p.a.” solution), for different exposure periods of 1 and 12 weeks, in addition to comparing the results with those not exposed to these conditions. Following this, standardized Double Cantilever Beam (DCB) tests were carried out to evaluate the influence of the aging processes on the adhesive’s mechanical properties and on the interlaminar fracture toughness of the composite material. From the static characterization, the critical Mode I energy release rate values were determined and used as a reference to define the experimental strategy in the fatigue tests. This allowed obtaining fatigue initiation curves (ΔG–N) and crack propagation curves (G–da/dN). The experimental results in the fatigue initiation phase were analyzed using a probabilistic model based on the Weibull distribution, enabling a more accurate description of the inherent variability of the delamination phenomenon.