[1] At the outbreak of the American Civil War in April 1861, Wheaton joined the 8th Illinois Infantry as a first sergeant.

Wheaton received a brevet (honorary promotion) to colonel on March 26, 1865, for his service in the campaign against Mobile, Alabama.

Wheaton was appointed brigadier general of volunteers at the outbreak of the Spanish–American War on May 27, 1898, and was placed in command of the 1st Brigade, 1st Division, Seventh Army Corps stationed in Miami.

Wheaton was then sent to the Philippines, where he was placed in command of a Provisional Brigade in the Eighth Army Corps during the Philippine–American War.

He was breveted to major general of volunteers on June 19, 1899, for gallantry in action against insurgent forces in Imus, Philippines.

A. Barnes, a soldier in the G Battery of the 3rd Artillery Regiment, wrote a letter to his brother describing the massacre: The town of Titatia was surrendered to us a few days ago, and two companies occupy the same.

Immediately orders were received from General Wheaton to burn the town and kill every native in sight; which was done to a finish.

Citation: Led the right wing of his regiment, and, springing through an embrasure, was the first to enter the enemy's works, against a strong fire of artillery and infantry.