Plymouth was one of the first Royal Navy ships to arrive in the South Atlantic following the Argentine invasion of the Falkland Islands and South Georgia. Plymouth alongside HMS Brilliant and HMS Endurance took part in the recapturing of South Georgia on April 28. Plymouth landed Royal Marines from her Westland Wasp helicopters and bombarded Argentine troop positions on the island. Later her Wasp helicopter took part in an attack on the ARA Santa Fe, which was badly damaged and later captured by Royal Marines.
After South Georgia was liberated, Plymouth rejoined the main task force, taking part in many operations before the landings at San Carlos Water. Plymouth supported troops on the ground by bombarding Argentine troop positions with her two guns. On June 8, a lone Plymouth was attacked by Dagger fighters of the Argentine Air Force, and Able seaman missileman Phil Orr managed to fire her Sea Cat missile system at them, claiming the shooting down of two aircraft. Later it was determined that no Dagger was lost in action that day. Plymouth was hit by bombs and cannon shells, causing considerable damage to the ship which was fixed by LMEM Robin Cunningham. She returned to Rosyth Dockyard after the war for repair and refit.
The following year, Plymouth served as the West Indies Guardship which included several days anchored off Belize.
Plymouth City Council had expressed an interest in HMS Plymouth, and the HMS Plymouth Preservation Trust undertook to raise the £250,000 needed to bring the warship back to her home city. It had been hoped that the frigate could be berthed at Millbay Docks, but the offer of a berth was withdrawn in January 2007 by Associated British Ports.