Robert D. Slayton was born around 1836 in New York to William M. Slayton and Miriam H. Wells. His father was a wagon maker and wheelwright who owned $300 of real estate and $300 of personal property by 1860. Slayton grew up and attended school in Harmony, New York. He married Helen Wilcox there on September 13, 1857, and their daughter Myra was born around 1866. By 1860, he was working as an inn keeper, and he owned $200 of personal property.
He enlisted in the Union army on July 30, 1862, and mustered in as a private in Company D of the 112nd New York Infantry on August 8. According to his service records, he was 5 feet, 9 inches tall, with dark hair and dark eyes. He was assigned to the Ambulance Corps in June 1863, and he was discharged for disability at Fortress Monroe, Virginia, on April 14, 1864.
He returned to New York after the war and settled in Cherry Creek. By 1870, he was working as a wagon maker, and he owned $500 of real estate and $250 of personal property. He applied for a federal pension in October 1873 and eventually secured one. They moved to Ashville, New York, in the 1870s, and by 1800, he was working as a bootman. He was unemployed for at least 6 months that year. They moved to Jamestown, New York, in the late 1800s, and he died there on December 19, 1905.