John P. Garrett was born around 1811 in Trenton, New York, to Cheney and Lorena Garrett. He married Elizabeth Savage, and they had at least four children: William, born in 1840; Edward, born around 1841; Cornelia, born around 1844; Ella, born in 1850; and George, born around 1858. They lived in Trenton, and Garrett worked as a farmer. By 1850, he owned $4,200 of real estate. A decade later, he owned $3,000 of real estate and $1,000 of personal property.
He enlisted in the Union army on September 13, 1862, and he mustered in as a private in Company E of the 97th New York Infantry. He apparently lied about his age, claiming he was born in 1818. According to his service records, he was 5 feet, 6 inches tall, with brown hair and blue eyes. The regiment took part in the Battle of Fredericksburg, the Battle of Chancellorsville, the Battle of Gettysburg, the Overland Campaign, the siege of Petersburg, and the Appomattox campaign. He mustered out on July 18, 1865.
He returned to Trenton after the war and resumed his work as a farmer. By 1870, he owned $4,600 of real estate. He applied for a federal pension in June 1880 and eventually secured one. In November 1899, he was admitted to the National Home for Disabled Volunteer Soldiers in Dayton, Ohio. He was suffering from “defective hearing,” “weak and intermittent” heart action, and the “debility of age.” He died of “Asthenia from Senectus” in Dayton on August 12, 1900.