Dunn was born into a prominent Hanover, Indiana family. He attended Hanover College and served as a private in the Mexican War. His brother, Williamson McKee Dunn, served as a congressman and later the Judge Advocate General of the Army. When the Civil War began, Dunn organized a company, which became part of the 9th Indiana Infantry Regiment. On April 24, 1861, he was promoted to the rank of captain. In July of 1861, Dunn was mustered out and became a captain in the 12th US Infantry. Later he served with the 21st US Infantry. At the Battle of the Wilderness, Dunn received breveted to ranks of major and lieutenant colonel for "gallant & meritorious" service. After the war Dunn remained in the regular army. In February 1873 he was promoted to major, while serving with the 8th US Infantry. Later Dunn served with the 12th US Infantry. Dunn was stationed in Oregon, Wyoming and Arizona, including Tucson and Ft Yuma. On June 29, 1878 Dunn retired from the army. During the last 16 years of his life, Dunn resided in Santa Monica California with two daughters. He died of appendicitis at his residence following surgery. Dunn is buried next to his son, Lt John Tipton Dunn.

Dunn was born into a prominent Hanover, Indiana family. He attended Hanover College and served as a private in the Mexican War. His brother, Williamson McKee Dunn, served as a congressman and later the Judge Advocate General of the Army. When the Civil War began, Dunn organized a company, which became part of the 9th Indiana Infantry Regiment. On April 24, 1861, he was promoted to the rank of captain. In July of 1861, Dunn was mustered out and became a captain in the 12th US Infantry. Later he served with the 21st US Infantry. At the Battle of the Wilderness, Dunn received breveted to ranks of major and lieutenant colonel for "gallant & meritorious" service. After the war Dunn remained in the regular army. In February 1873 he was promoted to major, while serving with the 8th US Infantry. Later Dunn served with the 12th US Infantry. Dunn was stationed in Oregon, Wyoming and Arizona, including Tucson and Ft Yuma. On June 29, 1878 Dunn retired from the army. During the last 16 years of his life, Dunn resided in Santa Monica California with two daughters. He died of appendicitis at his residence following surgery. Dunn is buried next to his son, Lt John Tipton Dunn.