Interlaminar delamination is one of the most hostile threats to the structural integrity of composite materials. Many failure criteria have been proposed for mixed-mode delamination. Most of existing criteria are not based on underlying failure mechanisms and are obtained through fitting the experimental data from various fracture toughness tests. In this study, a new mixed-mode delamination failure criterion is developed based on a characteristic plane approach and the Tsai-Wu strength theory for composite materials. The proposed failure criterion is based on the different failure mechanisms under pure mode I and mixed-mode loadings. One advantage of the proposed failure criterion is that it only requires two experimental measurements under pure mode I and pure mode II loading and all other mixed-mode failure can be predicted without additional fitting. Verification with extensive experimental data available in the literature is performed to demonstrate the validity of the proposed criterion. A general good agreement is observed between the model predictions and experimental observations. Following this, the proposed new criterion is compared with several existing failure criteria.