He was the 3rd mayor of Green Bay, Wisconsin, and served as a Union Army cavalry officer during the American Civil War.
That year, he formed a law partnership with Morgan Lewis Martin, and subsequently partnered with Timothy O.
In the first year of the war, he volunteered for service and was commissioned major of the 2nd battalion of the 2nd Wisconsin Cavalry Regiment.
[4] The 2nd Wisconsin Cavalry was involved in heavy campaigning in the western theater of the war, and assisted in the Siege of Vicksburg in 1863.
Major Eastman was promoted to lieutenant colonel in April 1864, but was forced to resign due to illness just two months later.