He enrolled at the University of Wisconsin in 1857[2] and taught school for a number of years, but he enjoyed farming and chose to make that his primary occupation.

[1] Though he was officially drafted early in the American Civil War, Warner later commented that his affairs were not sufficiently arranged to serve at that time, and provided a substitute.

[3] In 1864, he determined that he had made sufficient preparations and accepted a commission from Governor James T. Lewis to assist in raising men for the new 36th Wisconsin Infantry Regiment.

[5]: 824 They arrived in the midst of General Ulysses S. Grant's Overland Campaign and were directed to proceed to join the Army of the Potomac at Spotsylvania County, Virginia.

They arrived on May 18, one of the last days of the Battle of Spotsylvania Court House, and, on May 19, were attached to the 1st Brigade, 2nd Division, II Corps.

On June 1, a severe engagement began on the far left of the Union line, in the initial fighting of the Battle of Cold Harbor.

Warner's brigade, located near the right end of the Union line, was directed to make a demonstration against the enemy in an attempt to compel them to remain in position.

[5]: 826 That night, the 36th Wisconsin accompanied the movement of II Corps to the southeast to join the massing of forces for an attack on the Confederate right.

[5]: 827 After several days entrenched around Cold Harbor, II Corps was ordered to move again, this time across the James River, advancing to Petersburg.

[5]: 828  The attack stalled, command of the regiment devolved to Major Warner, and both sides began to retrench for what became the Siege of Petersburg.

The 36th Wisconsin, with II Corps, was ordered to make a feint towards Richmond, Virginia, to force General Lee to dilute the defense of Petersburg before the detonation of the mine.

The First Battle of Deep Bottom, which started on July 27, had the desired effect as Lee sent more forces north to reinforce Richmond.

They did not participate in the Battle of Lewis's Farm, but in the aftermath managed to occupy Confederate trenches approaching Petersburg.

The decisive Battle of Appomattox Court House occurred on April 9, 1865, and Colonel Warner had the honor of being present at the surrender of the Army of Northern Virginia.

He made another run for office in 1873 in Dane County's 2nd Assembly district, which then comprised the towns of Blooming Grove, Burke, Dunn and Windsor, and the city of Madison, but was defeated by the Reform Party candidate, Philo Dunning.

Warner remained active in the Republican Party of Wisconsin and was a political ally of Madison power-broker Elisha W. Keyes.

With his support, in 1877, Warner was elected Superintendent of the Poor by the Dane County Board of Supervisors for a three year term.