He attained the rank of brigadier general by brevet as a member of the Union Army during the American Civil War.

Returning to Kingston to administer his father's estate, Van Buren studied law, attained admission to the bar, and practiced.

Van Buren returned to the Army for the American Civil War, serving primarily as chief of staff to John Adams Dix as Dix carried out a series of senior commands; Van Buren advanced through the ranks to colonel, and received a brevet promotion to brigadier general in recognition of his superior service during the war.

[1] In 1843 he began attendance at the United States Military Academy;[1] he graduated in 1847 ranked 6th of 38 in his class, and was commissioned as a second lieutenant in the artillery corps.

[1] Van Buren remained on active duty after the 20th Regiment completed its initial period of service, and in August 1861 he joined the staff of John Adams Dix, then a major general, who commanded the Departments of Maryland and Pennsylvania.

[1] He later served as assistant adjutant of the Department of the East under Joseph Hooker, and in March 1865 he was promoted to brigadier general by brevet in recognition of his superior service during the war.

[3] He was also active in several business ventures, including a bluestone quarry near Kingston, which he leased to various operators, and which was the source for many of the paving stones used in New York City in the mid to late 1800s.