A quasi-static progressive damage model based on the fracture mechanics approach was developed for adhesively-bonded pultruded glass fiber-reinforced polymer (GFRP) joints. The model comprises the implementation in a numerical algorithm of a mixed-mode fracture failure criterion, experimentally developed using data acquired under pure Mode I and II and mixed-Mode I/II loading conditions. The bridging effect, as exhibited mainly by the R-curve behavior of the examined joints, was taken into account in the failure criterion. The numerical algorithm, assisted by finite element analysis for calculation of the strain energy release rate, was successfully employed for predicting the strength and the R-curve response of adhesively-bonded double-lap structural joints.