The Emerald Guard was formed in and around the town of New Market during May and early June of 1861. It was organized by a thirty-four year old Shenandoah County native named Marion Marye Sibert. and as it’s name implied was formed from the Irish laborers that worked in the Valley when the War began. The company would become among the most colorful and volatile companies of the famed “Stonewall Brigade”. “In their adopted sector,” one historian would write, “the Sons of Erin did not mesh easily with their conservative neighbors, most of whom were of German and Scotch-Irish descent. The Celts’ predilection for hard liquor and their affinity for world-class brawling at the least provocation engendered a definite air of notoriety.

Many of the Irishmen who joined the unit in May and June of 1861 were thought to be laborers who had been engaged on the construction of the Manassas Gap Railroad.
By the middle of May, the company elected its officers and non-commissioned officers (NCOs). Sibert naturally assumed the role of Captain of the Company. To compliment Sibert’s militia experience, Thomas C. Fitzgerald proved to be a “most valuable acquisition” and was elected 1st Lieutenant of the company. Prior to his immigration to the United States, Fitzgerald boasted prior military experience with the British Army during the Crimean War. For this reason, he was thought “well qualified for drilling the company.
The 33rd Virginia remained in the Stonewall Brigade in Thomas J. Jackson’s Second Corps until the restructuring of the Army of Northern Virginia after his death in the spring of 1863. It was placed under Richard Ewell’s command until the spring of 1864, when it dissolved following heavy losses at the Battle of Spotsylvania Court House.