This study performed an experimental modal analysis and investigated the mechanical properties of graphene nanoparticle (GNP)-reinforced, adhesively bonded double strap joints (DSJs). The DP270 structural adhesive was reinforced with graphene nanoparticles by using five different manufacturing methods and bulk specimens were prepared with 1%, 2% and 3% reinforcement by weight. The dispersion of graphene was observed by using scanning electron microscopy (SEM) because its efficient distribution in the adhesive is directly affected by the mechanical and modal properties of the modified polymer. Furthermore, the damping ratios and natural frequencies of the bulk specimens were also determined. Based on the dynamic characteristics and SEM observations, the most appropriate method to manufacture the joints was selected, and DSJs were prepared by using AA 2024-T3 aluminum alloy as the adherend. After that, the modal and tensile properties of the graphene-reinforced DSJs were determined. Consequently, it was observed that a graphene reinforcement ratio of 2% by weight showed a 36% increase in the damping ratio of the adhesive and a 23% increase in the damping ratio of the joint. In addition, it was observed that graphene reinforcement resulted in up to an 81% increase in the failure strength of the modified DSJs.