This paper considers the problem of multichannel through-wall radar (TWR) imaging from a probabilistic Bayesian perspective. Given the observed radar signals, a joint distribution of the observed data and latent variables is formulated by incorporating two important beliefs: low-dimensional structure of wall reflections and joint sparsity among channel images. These priors are modeled through probabilistic distributions whose hyperparameters are treated with a full Bayesian formulation. Furthermore, the paper presents a variational Bayesian inference algorithm that captures wall clutter and provides channel images as full posterior distributions. Experimental results on real data show that the proposed model is very effective at removing wall clutter and enhancing target localization.