Stephen S. Gregory was born in Unadilla, New York on November 16, 1849. He is the brother of Charles Noble Gregory, himself a distinguished writer on legal subjects. His family moved to Madison, Wisconsin in 1858. He was educated at the University of Wisconsin–Madison, receiving an A.B. in 1870, an LL.B. in 1871, and an A.M. in 1873.
In 1880, he married Janet M. Tappan, daughter of Arthur Tappan. The couple had three children together: Charlotte C. Gregory, Tappan Gregory, and Stephen S. Gregory, Jr.
He joined the firm of Tenney & Flower in 1879, with the firm shortly thereafter becoming Flower, Tenney & Gregory. He formed a new firm, Gregory, Booth & Flower in 1888. He founded a new firm in 1900, with his son Tappan becoming a partner.
Gregory's practice involved him in several high-profile cases. He represented Chicago in Illinois Central Railroad v. Illinois, 146 U.S. 387 (1892). He represented Patrick Eugene Prendergast after his 1893 assassination of Mayor of Chicago Carter Harrison, Sr.
Gregory died on October 24, 1920.
- Stephen Strong Gregory (6 ed.). American Bar Association Journal. p. 143.