Strain concentration is critically important for safety assessments of structural components. In the present work, a real-time and visible monitoring method for biaxial crack growth behavior using mechanochromic luminescence (MCL) was studied. 1,1,2,2-tetrakis(4-nitrophenyl)ethene (TPE-4N) is an organic mechanoresponsive luminogen (MRL). The crack growth behavior of 2024-T4 aluminum alloy was investigated under in-plane biaxial monotonic tension–tension loading with biaxiality ratios of λ = 0, 0.5, and 1.0. The surface of specimens was coated with a uniform TPE-4N film. It is remarkable that unexpected local strain concentration can be transformed into real-time and visible fluorescence ultraviolet irradiation. The fluorescence distribution obtained using the organic MRL method has a good agreement with the results using finite element method (FEM) simulation. The local plastic deformation near the crack tip causes fragments of crystalline TPE-4N film, inducing MCF in this region. Therefore, dynamic visualization of crack initiation and the crack growth path can be achieved. The present method may open up new opportunities for large-scale, full-field, and on-site structural health monitoring of crack growth in complicated structural components.