Reuben H. Dunn was born around 1833 in New Hampshire to Samuel and Abbie Dunn. He lived in Candia, New Hampshire, and worked as a shoemaker. He married Mary J. Morrill on March 15, 1855, and they had at least five children: John, born around 1855; Nellie, born around 1857; Cyrus, born around 1862; Cora, born around 1865; and Emma, born around 1870. They lived in Candia, and by 1860, he owned $200 of personal property.
Dunn enlisted in the Union army on August 15, 1862, and he mustered in as a private in Company I of the 11th New Hampshire Infantry on September 2. The regiment took part in the Battle of Fredericksburg, the Battle of the Wilderness, the Battle of Spotsylvania Court House, the Battle of Cold Harbor, the siege of Petersburg, and the Appomattox campaign.
He returned to Candia after the war. He applied for a federal pension in May 1869 and eventually secured one. By 1870, he owned $1,000 of real estate and $200 of personal property. His wife died in the late 1800s, and by 1890, he was living in Raymond, New Hampshire. He died there on March 12, 1909.