Gurnee was born in Haverstraw, New York and arrived in Chicago in 1836 after spending time in Michigan.[5] Once in Chicago, he established a tannery, which, by 1844, employed between thirty and fifty men.[6] He was a founding member of the Chicago Board of Trade. Prior to becoming the mayor of Chicago, Gurnee was the primary partner of Gurnee & Matteson, a saddlery and leather firm. Gurnee did well enough in this business, and in his tannery, that he amassed a large fortune before moving to New York City.[7]
Gurnee campaigned for the mayoralty on the issue of public ownership of the city's water supply. Once in office, he fought against the merger of the Illinois Central and Michigan Central railroads, originally planned to meet up south of the city.[8] He was elected to two terms, winning the mayoralty in 1851 and being reelected in 1852.
Gurnee unsuccessfully attempted to stage a return to the mayor's office in the 1860 mayoral election. He lost to "Long John" Wentworth, who had previously served a term as mayor as a Democrat, but had switched to the Republican Party.[9]