Obadiah Mead Knapp was born on October 23, 1840, in Greenwich, Connecticut, to Isaac Knapp. His father was a farmer who owned $6,000 of real estate and $1,000 of personal property. He grew up and attended school in Greenwich before enrolling at Yale College in 1860.
He left college after a year to join the Union army. He enlisted on September 29, 1861, and he mustered in as a corporal in Company I of the 10th Connecticut Infantry on October 2, 1861. He was discharged for disability on August 5, 1862. He resumed his studies at Yale until July 1863, when he rejoined the Union army as a hospital steward. He received a commission as a captain in the 121st USCT Infantry in March 1865. In August 1865, he became a captain in the 125th USCT Infantry, and he was promoted to major in 1866. He mustered out in October 1867.
Knapp settled in Philadelphia, Pennsylvania, after the war. He married Gertrude A. Palmer on March 18, 1868, and they had at least three children: Lewis, born on March 7, 1872; Mary, born around 1875; and Amos, born around 1879. They moved to North Castle, New York, in the 1870s, and he worked as a farmer there. He applied for a federal pension in October 1881 and eventually secured one. By 1893, he was suffering from pneumonia and neuralgia. He supported the Republican Party, and he described himself as a “pretty offensive partisan.” By 1900, they were living in their daughter Mary’s household in Butler, Pennsylvania. They moved to Wallingford, Connecticut, in the early 1900s, and he died there on May 26, 1921.