He served as a officer and brigadier general in the military Confederate States Army during the American Civil War (1861-1865), mainly in the Western Theater during the conflict.

[4] In the spring of 1862 he was transferred as a captain in the 29th Mississippi Infantry, and fought at the Battle of Shiloh (also known in the South as Pittsburg Landing) on April 6, where he was among 10,000 Confederate casualties.

[3] Brantley led his regiment (now part of the Confederate Army of Tennessee) during the Battle of Chickamauga from September 19–20, 1863, and with distinction in the Chattanooga Campaign that October and November.

[5] In his commander's report about the subsequent Battle of Lookout Mountain, Brantley was praised for his conduct: It is due in particular to commend Col. W. F. Brantley, Twenty-ninth Mississippi regiment and Lieut.-Col. McKelvaine, Twenty-fourth Mississippi regiment, for the skill, activity, zeal and courage I have ever observed in them under similar circumstances, but which in an especial degree signaled their actions on this occasion.

[1] In the inconclusive Battle of Resaca on May 13–15, Colonel Brantley was again noted for his performance, "commended for gallantry, after leading a charge on the enemy that repulsed Federal assaults three times."

During the Battle of Atlanta on July 22, 1864, his brigade commander, Col. Samuel Benton, was mortally wounded, hit in his chest and right foot by a shell.

At the Second Battle of Franklin on November 30, Brantley's command consisted of the 24th, 27th, 29th, 30th, and the 34th Mississippi Infantry regiments, plus a dismounted cavalry company.

[10] He was paroled on May 1 from Greensboro after the surrender ceremonies there of the second major Confederate Army to lay down their arms, and returned home to Mississippi.

The Weekly Clarion newspaper stated in November 1870 that it was the General’s attempt to bring to justice the party responsible for this murder that led to his own death.