People often rely more on their prior beliefs than the presented evidence when evaluating arguments. We investigate the cognitive mechanisms underlying this phenomenon. We hypothesise that when individuals encounter an argument that is congruent with their beliefs, it activates related information in memory. For belief-congruent arguments, people should therefore be more likely to both correctly recognise previously encountered information and incorrectly recognise new information as previously seen. To test this, we first investigated the effect of participants' beliefs about political claims on their evaluation of corresponding arguments that varied in quality. We then employed a surprise memory test to assess participants’ recognition memory for these arguments. While we replicated the finding that prior beliefs drive argument evaluations, prior beliefs did not affect memory performance for all arguments in the same way. Our results indicate that individuals may use prior beliefs to aid memory only when the memory task is difficult.