The Legislative Assembly of Upper Canada authorized the lighthouse in 1803, but construction did not begin until 1808. Builders quarried stone from Queenston for the base and later extended the tower in 1832 using Kingston stone. When completed in August 1809, the lighthouse stood close to the water's edge on what was then a far more exposed point. Sand has accumulated steadily since, so the tower now sits well inland - a measure of how the Toronto Islands themselves have shifted over two centuries. The light began as candles burning inside an oak and glass cage, graduating to sperm oil in 1832, coal in 1863, and finally electric light in 1916. A keeper's cottage - a two-story squared-log house clad in clapboard - stood alongside the tower until its demolition in 1950. When ships approached, the keeper would run up a flag to alert the Toronto harbour master across the water.

John Paul Radelmüller was born around 1763 in Ansbach, Germany, and spent twenty years as a servant in British royal households - first to the Duke of Gloucester, then the Duke of Kent. He accompanied the Duke of Kent to Halifax, Nova Scotia in 1799, eventually making his way to York (as Toronto was then known) by 1804. On July 24, 1809, Radelmüller was appointed keeper of the Gibraltar Point Lighthouse. For nearly six years, he tended the light, brewed his own beer, and lived in the keeper's cottage at the edge of the Great Lakes. He was approximately fifty-two years old on the night of his death. Recent scholarship by historian Eamonn O'Keeffe identified the two soldiers charged with his murder as John Henry and John Blueman, both Irishmen serving with the Glengarry Light Infantry - a regiment that had seen heavy action in the War of 1812, which had ended just weeks earlier.

The legend grew wilder over the decades. According to the popular version, the drunken soldiers chopped Radelmüller's body apart and scattered the remains to conceal their crime. In 1893, the lighthouse's fourth keeper, George Durnan, searched the grounds near the tower. He found part of a jawbone and fragments of a coffin, though it was impossible to prove definitively that they belonged to Radelmüller. O'Keeffe's research cast doubt on the more lurid details - contemporary evidence suggests the body was not mutilated. But the basic shape of the story held true: Radelmüller did die violently on January 2, 1815, and soldiers were indeed charged. Toronto historian Mike Filey captured the lingering uncertainty when he wrote that, regarding the truth of the keeper's demise, 'Your guess is as good as mine.' The lighthouse earned its reputation as one of Toronto's most haunted sites.

After Radelmüller's death, the lighthouse passed through a succession of keepers who tended the light for the next century and a half. William Halloway served from 1816 to 1831. James Durnan took over in 1832, beginning a family tenure that lasted until 1908 when his son George finally retired after fifty-four years of service. The original wooden lamp structure was replaced with steel in 1878. Metro Parks assumed operations in 1958, and the lighthouse was renovated in 1961-62. Now decommissioned and replaced by smaller automated lights at Humber Bay Park and Bluffer's Park, the Gibraltar Point Lighthouse stands as one of Toronto's oldest surviving structures. It opens occasionally for public tours, including during the annual Doors Open Toronto weekend, when visitors can climb the tower and look out over the harbor that Radelmüller once watched alone.