The medial prefrontal cortex (mPFC) resolves approach-avoidance conflicts and mediates associative processes required for learning to avoid threats. Dopamine (DA) projections from the ventral tegmental area (VTA) to the mPFC carry information about aversive outcomes that may inform prefrontal computations. However, the role of prefrontal DA in learning based on aversive outcomes remains poorly understood. Here, we used platform mediated avoidance (PMA) to study the role of mPFC DA in threat avoidance learning in mice. We show that activity within dopaminergic VTA terminals in the mPFC is required for signaled avoidance learning, but not for escape, conditioned fear, or to recall a previously learned avoidance strategy. Using a Rescorla-Wagner model fit to the behavior of individual mice, we discovered that VTA-mPFC activity drives experience-dependent transitions in the mode of learning. As mice learn PMA, changes in avoidance behavior were initially driven by experiences of shock and later by successful shock avoidance. Inhibition of VTA-mPFC terminals prevented this transition. Taken together, these data indicate that mPFC DA is necessary to rapidly form associations between predictive cues and actions that preempt aversive outcomes.