While signatures of attention have been extensively studied in sensory systems, the neural sources and computations responsible for top-down control of attention are largely unknown. Using chronic recordings in mice, we found that fast-spiking parvalbumin (FS-PV) interneurons in medial prefrontal cortex (mPFC) uniformly show increased and sustained firing during goal-driven attentional processing, correlating to the level of attention. Elevated activity of FS-PV neurons on the timescale of seconds predicted successful execution of behavior. Successful allocation of attention was characterized by strong synchronization of FS-PV neurons, increased gamma oscillations, and phase locking of pyramidal firing. Phase-locked pyramidal neurons showed gamma-phase-dependent rate modulation during successful attentional processing. Optogenetic silencing of FS-PV neurons deteriorated attentional processing, while optogenetic synchronization of FS-PV neurons at gamma frequencies had pro-cognitive effects and improved goal-directed behavior. FS-PV neurons thus act as a functional unit coordinating the activity in the local mPFC circuit during goal-driven attentional processing. Display omitted •Increased firing of mPFC PV interneurons is a signature of top-down attention•Attention is characterized by synchronization of mPFC PV neurons and elevated gamma•Local pyramidal neurons show gamma-phase-dependent rate modulation during attention•Synchronization of mPFC PV neurons at gamma frequencies has pro-cognitive effects A combination of electrophysiology and optogenetic manipulations reveal that inhibitory parvalbumin interneurons and gamma oscillations are central to prefrontal cortex's control of attention.