In 1861, French originally served as a chief of ordnance for the state of Mississippi before he was appointed to brigadier general in October. He received a promotion to major general in August 1862. He served in Virginia and North Carolina before he was sent to Jackson, Mississippi, and transferred to the Army of Tennessee. In October 1864, he commanded the Confederate forces in the Battle of Allatoona in Georgia, which resulted in a Union victory. In the same campaign, he led his division at the Battle of Nashville in December 1864, which resulted in another Union victory. Shortly after, he was relieved from duty for an eye infection. He returned to service at Mobile, Alabama, and he served until the surrender in April 1865.
