Romaine Alvord Barnes was born on October 6, 1840, in Niagara County, New York, to George and Adeline Barnes. His father was a farmer who owned $4,500 of real estate and $1,000 of personal property by 1860. The family lived in Cambria, New York, until around 1854, when they moved to Ridgeway, New York. By the early 1860s, he was working as a farmer.
He enlisted in the Union army on August 6, 1862, and he mustered in as a sergeant in Company A of the 151st New York Infantry on October 22 alongside his brother Eugene. According to his service records, he was 5 feet, 6½ inches tall, with dark hair and gray eyes. The regiment took part in the Gettysburg campaign. On April 2, 1864, he was promoted to 2nd lieutenant in the 31st USCT Infantry. The regiment took part in the Battle of Cold Harbor, the siege of Petersburg, and the Appomattox campaign. He was promoted to 1st lieutenant on February 9, 1865, and he mustered out on November 7, 1865.
He settled in Lockport, New York, after the war, and he married Jennie Crapsey around 1868. They had at least three children: Albert, born around 1870; Ida, born around 1872; and Clarence, born around 1875. Barnes worked as a farmer, and by 1870, he owned $6,000 of real estate and $1,500 of personal property. He remained in Lockport for the rest of his life, and he died there on February 10, 1920.