In 1856 McNair moved to Washington, Arkansas, and continued his business there until Arkansasseceded from the Union. McNair raised seven companies of infantry which was augmented with other volunteers and designated the 4th Arkansas Infantry.
Soon after the Battle of Pea Ridge McNair and his brigade were transferred east of the Mississippi River. McNair's brigade was sent to General Edmund Kirby Smith for his invasion of Kentucky and fought at the Battle of Richmond.
At the Battle of Chickamauga McNair's brigade participated in exploiting the break in the Union lines that turned the battle for the Confederates. During the fierce fighting McNair was wounded and both he and his brigade were sent to Mississippi for recuperation. In 1864 McNair was transferred to the Trans-Mississippi Department where he served for the remainder of the war.
Evander McNair died at Hattiesburg, Mississippi, and is buried at Magnolia Cemetery in Magnolia. His wife, Hannah Merrill McNair, a New York Yankee, preceded him in death in 1878 and is buried next to him.