Sylvanus E. Parker was born around 1830 in Rensselaer County, New York. He married Emily Tisdale on August 28, 1853, and the couple had no children. They lived in DeRuyter, New York, and he worked as a farm laborer. By 1860, they owned $400 of real estate.
He enlisted in the Union army on September 29, 1861, and he mustered in as a private in Company G of the 76th New York Infantry on October 9. The regiment took part in the Second Battle of Manassas, the Battle of Antietam, the Battle of Fredericksburg, the Battle of Chancellorsville, the Battle of Gettysburg, the Overland Campaign, and the siege of Petersburg. He reenlisted in March 1864, and he was promoted to sergeant that September. In January 1865, army officials transferred him to Company G of the 147th New York Infantry. He was wounded in the thigh at White Oak Road on March 31, 1865. Surgeons amputated his leg, but he died two hours after the amputation.