Isaiah Reed was born on February 12, 1840, in Howardsville, Albemarle County, Virginia. He eventually made his way to Buchanan, Pike County, Ohio, where he performed "ordinary farm work" for the father of man named James M. Dolahan.

Reed enlisted as a private in the Union army on June 15, 1863, at Washington Court House, Ohio, for a period of 3 years. He mustered into the 5th USCT Infantry Regiment later that day. His enlistment records describe him as 5 feet, 9 inches tall, with black hair, black eyes, and a black skin complexion. 

The regiment was stationed in Yorktown, Virginia, before taking part in General Isaac J. Wistar's expedition to Richmond in February 1864. After failing to capture the Confederate capital, the regiment help surround and besiege Petersburg from the summer of 1864 until the spring of 1865. In November 1864, Reed contracted a lung disease from lying on the damp, cold ground. He eventually recovered, and after the fall of Petersburg, the army sent the regiment to help capture Fort Fisher in North Carolina. The men then occupied Raleigh and Goldsboro as part of the federal army's Carolina's Campaign. Reed became a corporal on May 1, 1865, following the fall of Wilmington, North Carolina, one of the Confederacy's last major ports. On July 7, however, the army reported him "absent without leave" and demoted him to private. He mustered out on September 20, 1865.

Reed returned to Pike County, Ohio, after the war, and he married Amilia Bird on July 3, 1874. They had four children, including Willie E., born on July 5, 1875; Lizzie E., born on October 22, 1878; and Clarence, born on August 12, 1881. Reed suffered from cough, disease of lungs, and "malarial poisoning." However, he still worked as a farmer on land owned by James A. Steele. Reed also joined the Grand Army of the Republic. He applied for a pension in 1879 and began receiving one in 1890. By 1906, the government had increased his pension to $12 per month. He died of old age on June 23, 1910, in Springfield, Ohio, and was buried in the town's soldiers' cemetery. His widow Amilia applied for a pension for herself and her minor child, but she was unable to receive one.