St. John's has been deployed on missions throughout the Atlantic Ocean, to the Indian Ocean; specifically the Persian Gulf and Arabian Sea on anti-terrorism operations, to the north as far as Grise Fiord and to the Caribbean where she played a role in helping to stop the flow of illicit drugs to North America.

[5][6] To reflect the changing long term strategy of the Navy during the 1980s and 1990s, the Halifax-class frigates was designed as a general purpose warship with particular focus on anti-submarine capabilities.

[7] As built the Halifax-class vessels deployed the CH-124 Sea King helicopter, which acted in concert with shipboard sensors to seek out and destroy submarines at long distances from the ships.

[7] As built, the anti-shipping role is supported by the RGM-84 Harpoon Block 1C surface-to-surface missile, mounted in two quadruple launch tubes at the main deck level between the funnel and the helicopter hangar.

[5][7] For anti-aircraft self-defence the ships are armed with the Sea Sparrow vertical launch surface-to-air missile in two Mk 48 Mod 0 eight-cell launchers placed to port and starboard of the funnel.

[7] A Raytheon/General Dynamics Phalanx Mark 15 Mod 21 Close-In Weapon System (CIWS) is mounted on top of the helicopter hangar for "last-ditch" defence against targets that evade the Sea Sparrow.

Further improvements, such as modifying the vessel to accommodate the new Sikorsky CH-148 Cyclone helicopter and satellite links will be done separately from the main Frigate Equipment Life Extension (FELEX) program.

The existing 57 mm Mk 2 guns were upgraded to the Mk 3 standard and the Harpoon missiles were improved to Block II levels, the Phalanx was upgraded to Block 1B and the obsolete Sea Sparrow system was replaced by the Evolved Sea Sparrow Missile.

The ship was launched on 26 August 1995 and commissioned into the Canadian Forces on 26 June 1996 in St. John's, and carries the hull classification symbol FFH 340.

[10] On 7 August 1997 the frigate joined NATO's Standing Naval Force Atlantic (STANAVFORLANT), returning to Canada on 18 December.

[12] In 2008, the vessel took part in Operation Caribbe, Canada's contribution to an ongoing U.S.-led, multinational effort to interdict drug trafficking in the international waters of the Caribbean Basin and eastern Pacific Ocean.

[citation needed] In September 2008, the frigate was sent to Haiti, carrying 350 tonnes of food and relief supplies after the nation had been hit by four hurricanes.

[17][18] During this deployment, the Joint Interagency Task Force South based out of Key West, Florida, coordinated the joint efforts in allowing the US Coast Guard to make 38 arrests, and seized a total of 10,902 kg (24,035 lb) of cocaine and 1,144 kg (2,522 lb) of marijuana, equating to more than US$223 million.

[27] In September 2017, St. John's was deployed the Caribbean Sea to bring relief aid to Turks and Caicos after Hurricane Irma swept through the region.

[29] However, the frigate was dispatched later that month to bring humanitarian aid to Dominica after Hurricane Maria devastated that island.

[31] The frigate returned to Halifax on 23 July, having participated in naval exercises in the northern Atlantic Ocean and Baltic and Mediterranean Seas.