John W. Sanborn was born on April 4, 1836, in Somersworth, New Hampshire, to Solomon Sanborn. His father was a farmer who owned $700 of real estate and $300 of personal property by 1860. He grew up and attended school in Tamworth, New Hampshire, and by 1860, he was a medical student.
He enlisted in the Union army on December 6, 1861, and he mustered in as a private in Company G of the 2nd United States Sharpshooters Battalion on December 12. According to his service records, he was 5 feet, 10 inches tall, with brown hair and blue eyes. The regiment took part in the Peninsula campaign, the Second Battle of Manassas, the Battle of Antietam, and the Battle of Fredericksburg. He was discharged for disability on February 3, 1863.
He returned to Tamworth after leaving the army, and he married Lucretia Buttles on April 11, 1866. They had at least three children: Rennie, born around 1867; Lapha, born around 1873; and Charles, born around 1878. He worked as a farmer, and by 1870, he owned $1,000 of real estate and $500 of personal property. His father died in the 1890s, and by 1900, he was living in his daughter Rennie’s household in Needham, Massachusetts. He died there of chronic nephritis on July 8, 1901.