Merritt Barber was born on July 31, 1835, in Pownal, Vermont, to Benjamin and Caroline Barber. His father was a farmer who owned $12,000 of real estate and $200 of personal property by 1860. He grew up and attended school in Pownal, and he attended Williams College. He married Catherine Roberts on June 20, 1859, and their daughter Sarah was born around 1860. By the early 1860s, he was working as a lawyer.
He enlisted in the Union army on June 2, 1862, and he mustered in as a 1st lieutenant in Company E of the 10th Vermont Infantry two months later. According to his service records, he was 5 feet, 7 inches tall, with brown hair and blue eyes. He was promoted to captain in July 1864, and he mustered out on May 20, 1865.
In 1866, he received a commission as a 2nd lieutenant in the 16th United States Infantry. His wife died in 1865, and he married Delilah Fowler around 1867. The couple had no children. By 1870, he was stationed in Grenada, Mississippi, and he owned $1,000 of real estate and $5,000 of personal property. He was promoted to captain around 1879 and to colonel around 1896. He retired around 1900, and he died in Watervliet, New York, on April 19, 1906.