Laid down by Harland and Wolff, Belfast, as HMS Minotaur, she was presented to the RCN and, on 26 Apr 1945, commissioned at Belfast as HMCS ONTARIO. She was completed on 25 May 1945, and after trials and workups, left the Clyde River on 02 Jul 1945 for the Pacific via the Mediterranean and the Suez Canal. ONTARIO joined the 4th Cruiser Squadron, British Pacific Fleet, too late to see war service, but was employed in a variety of duties which took her to Hong Kong and Manila. She arrived at Esquimalt on 27 Nov 1945 for refit.
From the memoirs of Cdr Bernard Lake: When ONTARIO was still in the UK the crew wanted to put a maple leaf on her funnel but Capt. Grant would not allow it until after they joined the British Fleet in the Med and passed work-ups with them. On completion of WUPS, when ONTARIO departed Malta enroute to the Suez, she was sporting a maple leaf on her after funnel.
In Oct 1948, ONTARIO was joined by the destroyers CAYUGA, ATHABASKAN, CRESCENT and the frigate ANTIGONISH in sailing to Pearl Harbor, Hawaii; the largest deployment of the Royal Canadian Navy following the war. In Jan 1949, ONTARIO took part in the largest training cruise by the Royal Canadian Navy to that date which included the aircraft carrier MAGNIFICENT, the destroyers HAIDA, ATHABASKAN and the frigate ANTIGONISH. The group, designated CTF 215, participated in naval exercises with US and British vessels in the Caribbean Sea. In Feb 1951, ONTARIO sailed to Australia, taking part in joint naval exercises with the Royal Australian Navy. On the way the ship made several port visits, returning to Canada in June. In Oct 1951, ONTARIO sailed to the east coast where after arrival, Princess Elizabeth and Prince Philip, Duke of Edinburgh sailed on the cruiser from Sydney, Nova Scotia, through the Cabot Strait to Newfoundland during the Royal Visit. She returned to Esquimalt following the tour, arriving in December. From Sep to Dec 1952, ONTARIO sailed around South America on a training cruise, making several port visits. While entering the harbour at Buenos Aires, she was overtaken by the merchant vessel SS Arauco and struck amidships. The ship continued on her cruise until arriving at Rio de Janeiro on 6 November. There it was found that the starboard propellers were damaged. The outer propeller was removed and repairs were made to the inner one. After nearly two weeks at Rio de Janeiro, ONTARIO was forced to return to Esquimalt at a reduced speed.
On 15 Jun 1953 ONTARIO took part in the Fleet Review to celebrate the Coronation of Queen Elizabeth II. In Jan 1954, ONTARIO began a training cruise across the Pacific, visiting Australia, New Zealand and Tonga before returning to Esquimalt in April. ONTARIO performed a three-month training cruise to Australia and New Zealand in early 1955, returning to Canada on 02 Apr 1955. She then departed on 25 Apr1955 for a four-month cruise of Europe. Late that year she departed Esquimalt for a 2-month summer training cruise along the coasts of North and South America, going as far south as Ecuador. She returned to port on 10 August after meeting the Second Canadian Escort Squadron off the coast of California.
ONTARIO was paid off on 15 October 1958. The ship was sold to a west coast firm which began but did not finish the job of breaking up the ship at Vancouver. The ship was resold, along with HMCS Quebec to Mitsui and Co. of Japan. She arrived at Osaka for breaking up on 19 November 1960.