St Lawrence had her keel laid on 12 April 1814, and was launched on 10 September 1814. British naval commodore Sir James Lucas Yeo commissioned her as his flagship, with Captain Frederick Hickey as Flag Captain, in the Kingston Royal Naval Dockyard in Kingston, Upper Canada. The ship cost Britain £500,000 or over CA$120 million in today’s dollars.
At the time, Lake Ontario was effectively landlocked for any but the smallest vessels, due to shallow water and rapids on the St. Lawrence River downstream and Niagara Falls upstream. As a result, warships operating on Lake Ontario had to be built on site, either in Kingston or in the American naval dockyards at Sackets Harbor, or converted from merchant ships already operating in the lake.
Control of the lake, which was the most important supply route for the British for military operations to the west, had passed back and forth between the Americans and the British over the course of the war. The construction of a first rate ship of the line, in a campaign that had been dominated by sloops and frigates, gave the British uncontested control of the lake during the final months of the war. HMS St Lawrence never saw action, because her presence on the lake deterred the U.S. fleet from setting sail.
After the war ended in 1815, the ship was decommissioned. In January 1832, the hull was sold to Robert Drummond for £25. Between May and August, the hull was towed out of Navy Bay. It later formed the end of a pier attached to Morton’s Brewery in Kingston and was used as a storage facility by the brewery, for cordwood among other materials. Later, it was sunk in 30 feet (9.1 m) of water close to shore at 44°13′14″N 76°30′18″W and is now a popular diving attraction.