[2] In 1847 Whitaker volunteered for service during the war with Mexico, and was commissioned a second lieutenant in the 6th Kentucky Infantry Regiment beginning on October 1.

Later he was elected as a legislator to the Kentucky General Assembly, serving until the American Civil War was well underway.

[4] On June 25, 1863, Whitaker was promoted to brigadier general, and given brigade command in the Army of the Cumberland that August.

He participated in the inconclusive Battle of Resaca that spring, and received his last Civil War wound there on May 15 when he was injured by the concussion of an artillery shell which exploded nearby.

[3] On March 13, 1865, Whitaker was appointed a brevet major general for his actions near Atlanta, Georgia, on that date.

Whitaker died at the age of 63 in Lyndon, Kentucky, supposedly in full mental health, and was buried in Shelbyville's Grove Hill Cemetery.