William Glover Gage was born on April 11, 1847, in Italy Hill, New York, to Dewitt Clinton Gage and Catherine Glover. His father was a lawyer who owned $2,000 of real estate and $250 of personal property by 1860. The family lived in Gorham, New York, until around 1855, when they moved to Saginaw, Michigan.
Gage enlisted in the Union army on September 6, 1862, and he mustered in as a corporal in Company C of the 7th Michigan Cavalry on November 13. Confederate forces captured him on July 3, 1863, in the Battle of Gettysburg. He received a parole on August 6, and he returned to his regiment on September 15, 1863. The regiment took part in the Battle of the Wilderness and the Appomattox campaign. He remained devoted to the Union, writing that "I did not come here for promotion but to fight for my country." He was eventually reduced to the ranks, and he mustered out on March 17, 1865.
He attended the University of Michigan after the war, and he was admitted to the bar in 1873. He married Alice Sanborn around 1874, and they had six children, including: Catherine, born around 1875; Walter, born around 1876; George, born around 1879; Alice, born around 1884; and Louise, born around 1887. He supported the Republican Party, and President Chester A. Arthur appointed him postmaster for East Saginaw in 1883. He became city attorney in 1894 and reportedly filled the position with “credit and success.” He applied for a federal pension in February 1909 and eventually secured one.
His wife died in the early 1900s, and he married Eleanor B. Richardson on April 22, 1911. They had at least two children: Glover, born around 1913; and Ellen, born around 1918. Gage died of arteriosclerosis in Saginaw on July 27, 1924.