During the American Civil War, he recruited a company of the 37th Virginia Infantry, but failed to win re-election as captain, and ultimately moved to Texas in 1872 and re-established his practice.

[5]: 467  Although he failed to win re-election, Washington County voters elected him and fellow Unionist John Arthur Campbell as their delegates to the Virginia Secession Convention of 1861, defeating pro-secessionists William Y.C.

After Virginia's voters also ratified secession, and Confederate troops won at the First Battle of Manassas in July 1861, Grant recruited the King's Mountain Rifles in Abingdon and accepted a commission as its captain.

His unit refused to re-elect him during the April 1862 reorganization, instead promoting Sergeant William F. Duff to captain of Company H.[7]: 30, 115 Grant moved his family to Austin, Texas in 1872.

[6]: 783  Virginia farmers had endured two seasons of terrible crops, and by 1880 his parents had also moved to Abbeville County, South Carolina to live with his sister and a grandson.