Oliver Rawson Post was born on September 16, 1832, in Connecticut. He married Mary Holcomb on April 8, 1857, and they had at least four children: Harry, born around 1858; Emma, born around 1859; Hawley, born around 1861; and Frank, born around 1863. They lived in Hartford, Connecticut, and Post worked as a printer. By 1860, he owned $100 of personal property.
In 1862, he received a commission as a 1st lieutenant in Company C of the 20th Connecticut Infantry. He was promoted to captain on February 24, 1863. The regiment took part in the Battle of Chancellorsville, the Battle of Gettysburg, and the Atlanta campaign. He was wounded in the Battle of Peachtree Creek on July 20, 1864, and he died near Atlanta, Georgia, the following day.