In the early 1880s Gardiner worked for prominent and respected Toronto photographers, first Thomas E. Perkins and then Samuel J. Dixon.
Times were apparently not good and by 1890 Gardiner is no longer listed in the city directory as a photographer, but as a "fruitier" with his wife Louise.
His earliest Mackinac images date to 1896, the year he opened his gallery in the studio formerly occupied by the Foley Brothers in the Marquette Building at corner of Fort and Main Streets.
Gardiner was drawn to the resort life, for at about the same time he came to Mackinac Island he began spending his winters in Daytona, Florida.
Thus, at the turn of the twentieth century the course of Gardiner's life was set, with a summer studio on Mackinac Island and a winter one in Daytona.
Daytona appears to have been his place of primary residence after 1905 (he remained in the Detroit residential listings until 1905), where he was active in civic affairs.
Along with his son Marshall, he was involved in other real estate ventures including purchasing the Colony House (Palmetto) Hotel.
He developed a deep interest in early American architecture and decorative arts and became a pioneer of the Colonial Revival and preservation movements.
Gardiner likely began producing his hand-colored photographs of Mackinac Island and Florida in the early twentieth century.
Gardiner continued operating his studio and shop throughout World War I, the Roaring Twenties and into the Great Depression.
On October 22, 1935, on his annual autumn journey from Mackinac to Daytona, William H. Gardiner died of a heart attack.
The studio and shop on the second floor of the Fenton Building on Mackinac Island remained property of the family until Louise and Marshall Gardiner's deaths in 1942, within days of each other.