Robert D. Coxe was born on June 29, 1840, in Pennsylvania to James and Jane Coxe. His father was a clerk who owned $700 of personal property by 1860. Coxe grew up and attended school in Philadelphia, Pennsylvania, and he studied law at the University of Pennsylvania.
He enlisted in the Union army in 1861 and mustered in as a private in Montgomery’s Pennsylvania Heavy Artillery Company. He mustered out after 3 months. He enlisted again on September 12, 1862, and he mustered in as a private in Company D of the 7th Pennsylvania Militia Infantry. He mustered out two weeks later, on September 26, 1862. He enlisted a final time on June 18, 1863, and he mustered in as a corporal in Company D of the 32nd Pennsylvania Militia Infantry. He mustered out on August 1, 1863.
Coxe worked as a lawyer in Philadelphia, and he lived in his parents’ household until at least 1880. He married Anna Richards Colwell on February 4, 1882. His wife probably died in the late 1800s. He applied for a federal pension in August 1906 and eventually secured one. By 1910, he was living with three of his sisters in Glenolden, Pennsylvania. He died there of cirrhosis of the liver on July 26, 1917.