Flight, an active fear response to imminent threat, is dependent on the rapid risk assessment of sensory information processed by the cortex. The thalamic reticular nucleus (TRN) filters information between the cortex and the thalamus, but whether it participates in the regulation of flight behavior remains largely unknown. Here, we report that activation of parvalbumin-expressing neurons in the limbic TRN, but not those in the sensory TRN, mediates flight. Glutamatergic inputs from the cingulate cortex (Cg) selectively activate the limbic TRN, which in turn inhibits the intermediodorsal thalamic nucleus (IMD). Activation of this Cg→limbic TRN→IMD circuit results in inhibition of the IMD and produces flight behavior. Conversely, removal of inhibition onto the IMD results in more freezing and less flight, suggesting that the IMD may function as a pro-freeze center. Overall, these findings reveal a novel corticothalamic circuit through the TRN that controls the flight response.