General Davidson assumed command of the 3rd Brigade, 2nd Division, IV Corps during the Peninsula Campaign. He fought at the battles of Yorktown and Williamsburg. During the Seven Days Battles he received brevet promotions in the Regular Army for his service at Gaines' Mill and Golding's Farm. Shortly after the culmination of the Seven Days' fighting, Davidson was transferred to the Trans-Mississippi Theater where he was placed in command of the Dist. of St. Louis. From December 3, 1862 to March 26, 1863 he was also in command of the so-called Army of Southeast Missouri until much of his army was transferred to Ulysses S. Grant in preparation for the Vicksburg Campaign. He retained command of the Dist. of St. Louis until June 16, 1863 when he briefly commanded the Dist. of Southeast Missouri.