Imagine briefly losing your friend in a crowd: As you scan one face after another, you compare each input to a mental image of your friend’s face. This process spans multiple cognitive domains, from perception to working memory and visual search. Early visual cortex (EVC), the primary cortical site for processing visual inputs, has been implicated in the maintenance of mental visual representations. An outstanding question is why? We hypothesize that EVC is recruited for mental representations to serve as a comparison circuit, matching mental content to incoming sensory information in a visual format native to EVC. To test this, we collected fMRI data while participants (N=5) remembered the direction of a coherent random dot motion (RDM) stimulus for 8 minutes. During this period, participants saw 48 new RDM stimuli with independent motion directions and were cued to either compare a probe’s motion direction to the one they were holding in mind, or to withhold a comparison. Results show that BOLD responses for comparisons were higher than for non-comparisons throughout EVC. Importantly, making a comparison also rendered the motion direction held in mind significantly more decodable. This suggests that EVC is recruited to represent mental content when it needs to be compared to visual input. The role of EVC as a comparison circuit highlights that memories are typically stored for use, and that a broader cognitive context must be considered in order to accurately uncover how the brain represents mental content.