Abstract: Blind face restoration focuses on restoring high-fidelity details from images subjected to complex and unknown degradations, while preserving identity information. In this paper, we present a Prior-based Latent Transformation approach (PLTrans), which is specifically designed to learn a degradation-unaware representation, thereby allowing the restoration network to effectively generalize to real-world degradation. Toward this end, PLTrans learns a degradation-unaware query via a latent diffusion-based regularization module. Furthermore, conditioned on the features of a degraded face image, a latent dictionary that captures the priors of HQ face images is leveraged to refine the features by mapping the top-$d$ nearest elements. The refined version will be used to build key and value for the cross-attention computation, which is tailored to each degraded image and exhibits reduced sensitivity to different degradation factors. Conditioned on the resulting representation, we train a decoding network that synthesizes face images with authentic details and identity preservation. Through extensive experiments, we verify the effectiveness of the design elements and demonstrate the generalization ability of our proposed approach for both synthetic and unknown degradations. We finally demonstrate the applicability of PLTrans in other vision tasks.