[1][2] Jackson was then a member of the New York State Bar Association in 1860 and would begin actively practicing his legal career before the outbreak of the American Civil War.

At the outbreak of the war, Jackson volunteered to be Aide-de-Camp for Brigadier General Robert Anderson.

[1] Around the end of 1861, Jackson was made a part of William B. Franklin's general staff after Kearny was killed at the Battle of Chantilly and on August 20, 1862, was promoted to captain.

Jackson was then promoted to full colonel as well as brevetted Brigadier General on March 13, 1865, for "faithful and meritorious services in the field".

He was also a member of the Society of Political Reform and an active participant in the removal of Police Commissioner Gardner and Oliver Charlick.