PS Colin Travi was found by the Independent Police Complaints Commission to have a case to answer for gross misconduct after punching a man at Abingdon police station on August 18 2016.
CCTV footage showed that PS Travi punched the man in the head four times while attempting to restrain him alongside two other officers.
The blows to the head caused the man to lose consciousness and require medical treatment in hospital.
The hearing concluded that although it was necessary to use force in the circumstances, the strikes to the head were neither reasonable or proportionate.
Operations Manager Colin Dewar said: “Following a thorough and independent investigation by the IPCC, the disciplinary process has found that this officer breached the standards of professional behaviour expected of him.
“This use of force was simply unacceptable and I support the decision of the panel to dismiss PS Travi following a misconduct hearing.”