He graduated from Western Reserve College in Cleveland in 1850 and quickly moved west to Kenosha, Wisconsin, where he studied law in the office of Frederick S. Lovell and was admitted to the bar.
They then crossed the Ohio River to Covington, Kentucky, where the regiment was issued their arms and organized into the brigade of General Philip Sheridan.
[5]: 687 They were there ordered to march quickly to the defense of Louisville and attach to the Division of General Lovell Rousseau, in the Army of the Ohio.
[5]: 687 The 21st Wisconsin arrived in Louisville just in time to join the march into interior Kentucky that resulted in the Battle of Perryville on October 8, 1862.
On October 29, the regiment marched to Bowling Green and then to Mitchellville, Tennessee, to defend a railroad supply route.
Throughout this march and guard duty, the regiment suffered further from exposure, as they had left most of their camp equipment at Louisville before Perryville.
[5]: 688 They marched to Nashville, Tennessee, in December and their division was attached to the XIV Corps in William Rosecrans' Army of the Cumberland.
They camped at Nashville until the end of December, when they set out to confront Braxton Bragg's Army of Tennessee at Murfreesboro.
[4]: 114 In June 1863, the Army of the Cumberland set out for Tullahoma, with the strategic purpose of holding Bragg's attention and preventing him from sending forces to the relief of Vicksburg.
XIV Corps, now under the command of General George Henry Thomas, was ordered to probe Hoover's Gap, one of several passes through the Highland Rim, which the Union would need to secure to make its advance.
[5]: 689 In September, the 21st Wisconsin crossed the Tennessee River, along with XIV Corps, as part of Rosecrans's elaborate plan to surround Chattanooga.
XIV Corps proceeded to the Dug Gap en route to Lafayette, Georgia, where, unknown to the Union forces, Bragg was preparing to destroy their lead division.
Bragg's orders, however, were not carried out by the Confederate officers at the front, and the Union force under James S. Negley detected the danger and withdrew.
[5]: 690 Captain Walker lead the remainder of the regiment back to Chattanooga, where they rejoined the rest of the Union Army.
[5]: 691 At Pumpkin Vine Creek during the Battle of Dallas on May 27, the 21st Wisconsin scattered a band of Confederate skirmishers and occupied a strategic hill, where they were under fire for six days during the siege.
On June 27, 1864, the 21st Wisconsin joined the assault on Kennesaw Mountain, with their division assigned to support the attack on Cheatham Hill.
During the Battle of Peachtree Creek, the 10th and 21st Wisconsin regiments, under Colonel Hobart, critically drove back a Confederate attack.
The Confederates made attempts to raid at the rear of the Union army and Sherman pursued him briefly to Gaylesville, Alabama, but did not engage in battle—Major Walker was in command of the regiment through this campaign, as Major Fitch had taken leave to get married.
[5]: 696 After the war, Walker returned to his law practice, but due to poor health soon retired to a farm in Manitowoc Rapids, Wisconsin.