Daniel S. Mann was born around 1834. By the early 1860s, he was living in New York. He enlisted in the Union army in early 1863, and he served as a 1st lieutenant and aide-de-camp to General Daniel Ullman. In early 1865, he became a 1st lieutenant in the 38th USCT Infantry. He was promoted to captain on May 4, 1866, and he mustered out on January 27, 1867. He returned to New York after leaving the army. He applied for a federal pension in July 1871 and eventually secured one. He died sometime after July 1871.