Widebody Transport
Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Critical
Flight Crew Returned To Departure Airport; General Maintenance Action
Aircraft
On taxi out; the CA's (Captain) trim switch was tested per the MEL and was used to set the takeoff trim. After takeoff on initial climb out; the CA attempted to engage the autopilot without success. However shortly after that; the CA verbalized that his trim switch was also not working now. CA was using considerable forward pressure to keep the nose down and ultimately had to pull the power back to better control the aircraft. We quickly agreed we needed to return to ZZZ due to controllability concerns. CA continued to hand fly while I coordinated with ATC and set up for an otherwise uneventful return to landing at ZZZ.[Station Maintenance] was able to duplicate the problem on the ground after the event. The faulty FO (First Officer) trim switch was locking out the CA's trim switch and tripping the autopilot.
Air carrier First Officer reported pitch control problems after takeoff due to a trim switch failure.