Greble, John T. was born on January 19, 1834 in Philadelphia, Pennsylvania, United States. Son of Edwin and Susan Greble.
Graduated from the United States Military Academy, 1854.
Commissioned Second lieutenant artillery United States Army, 1854, stationed Newport Barracks, Florida, 1854-1856, explored lakes of area, served against Seminole Indians. Assistant professor ethics and English, United States Military Academy, 1856-1860. Promoted First lieutenant, 1859.
Joined regiment at Fortress Monroe, Virginia, 1860. Transferred to construct batteries and instruct volunteers in artillery, Newport News, Virginia, 1861. Ordered by General Benjamin F. Butler to lead attack against Big Bethel, Virginia, 1861.
Married Sarah B. French, August 4, 1858, 2 children.