John Keller was born on August 14, 1836, in present-day Germany to Adam and Phebe Keller. He immigrated to America around 1856, and by 1860, he was working as a farm laborer in Lysander, New York. He enlisted in the Union army on September 21, 1861, and mustered in as a private in Company B of the 75th New York Infantry on November 26. Confederate forces captured him in the Second Battle of Sabine Pass on September 8, 1863, but he was paroled the following month and rejoined his regiment. He mustered out in Auburn, New York, on November 25, 1864.
Keller settled in Conquest, New York, after leaving the army, and he married Regina Schatz around 1865. They had at least eight children: George, born around 1867; Anna, born around 1868; Frank, born around 1870; William, born around 1872; Minnie, born around 1876; Phillip, born around 1878; Katie, born around 1880; and Frederick, born around 1883.
By 1870, Keller was working as a farm laborer in Cato, New York, and he owned $150 of personal property. They moved to Port Byron, New York, in the 1870s, and by 1880, he was working as an “iron moulder.” He applied for a federal pension in July 1890 and eventually secured one. His wife Regina died around 1895. In 1900, he was living in Galen, New York, with his three youngest children. He died in New York in 1909.