John McConihe was born on September 4, 1834, in Troy, New York, to Isaac and Sarah McConihe. His father was a lawyer who owned $40,000 of real estate. He grew up and attended school in Troy, and he moved to the Nebraska Territory sometime in the 1850s. By 1860, he was working as a lawyer in Omaha, Nebraska, and he owned $6,000 of real estate and $500 of personal property.
He received a commission as a captain in Company G of the 1st Nebraska Infantry on June 15, 1861. The regiment took part in the Battle of Fort Donelson and the Battle of Shiloh. He was shot in the arm at Shiloh, and the Minié ball fractured a bone. He eventually recovered, and he became a lieutenant colonel in the 169th New York Infantry on September 23, 1862. He was promoted to colonel on February 13, 1864, and he died in the Battle of Cold Harbor on June 1, 1864.