This work explores the postbuckling behavior of a marine stiffened composite plate in the presence of initial imperfections. The imperfection shapes are derived from buckling mode shapes and their combinations. Thereafter, these imperfection shapes are applied to the model, and nonlinear large deflection finite element and progressive failure analyses are performed in ANSYS 18.2 software. The Hashin failure criterion is employed to model the progressive failure in the stiffened composite plate. The effect of the initial geometric imperfection on the stiffened composite plate is investigated by considering various imperfection patterns and magnitudes. Results show that when the magnitude of the imperfection is 20 mm, the ultimate strength of the stiffened composite plate decreases by 31%. Moreover, global imperfection shapes are found to be fundamental in determining the ultimate strength of stiffened composite plates and their postbuckling.