As a major general, he received recognition for delaying the advance of Maj. Gen. George B. McClellan's Army of the Potomac, during the 1862 Peninsula Campaign, as well as recapturing Galveston, Texas the following year.

In the Peninsula Campaign, he stalled McClellan's Army of the Potomac outside Yorktown, allowing Maj. Gen. Joseph E. Johnston to arrive with reinforcements, organize a retreat, and defend the Confederate capital, Richmond.

He spent the remainder of the war administering the District of Texas, New Mexico, and Arizona and the Department of Arkansas; in his tenure, Magruder lifted the naval blockade over Galveston and recaptured the city in 1863.

Magruder's father Thomas was from a family of Scottish plantation owners; on June 22, 1797, he married Elizabeth Bankhead, the eldest daughter of "noted millers" in Albemarle County.

His family occasionally traveled with Magruder during his various assignments but, because of the unfavorable conditions in the various remote locales, Henrietta found it more practical to live in Baltimore where she could raise their children and stay close to her business interests.

[10] On a request to the United States Department of War, Magruder arranged a transfer to the 1st Artillery with Albert Miller Lea, a correspondent from West Point, to stay close to Henrietta.

[11] The 1830s for Magruder, however, were largely regulated to garrison duty in North Carolina, Maryland, and Florida; the uneventful aspects of these assignments granted him time to study law and pass the bar examination.

[12] The adverse northern climate found at his latest post, the Hancock Barracks in Maine, contributed to a bronchial infection, he had seen no military action, and felt slighted by the lack of recognition for organizing crucial supplies during the Second Seminole War.

[13] In August 1845, Magruder volunteered for assignment in Corpus Christi, Texas, to join General Zachary Taylor's army there, occupying the former republic; the US was on the verge of war with Mexico over the question of annexation.

[14][15] On April 18, 1847, Magruder served with "zeal and ability", in General Winfield Scott's expedition, under heavy fire and turned Mexican artillery against them at Cerro Gordo, for which he was praised by his superiors and brevetted to major.

Magruder—lightly wounded—ordered the first shots in the early morning on the 13th and offered pursuit, despite superior Mexican numbers, to capture the Anzures, Veronica, and Belen intersection—a crucial crossroads that would block efforts by General Santa Anna to relieve the palace.

[22] Historian Edward A. Pollard noted that Magruder was recognized as one of the lead artillerists in the army: "It was in the rapid and effective management of field-pieces, and the combinations with which they were applied to accomplish immediate and important results, that his genius shone"; Magruder's experience helped him convince the War Department in 1860 to accept a revised version of his logistics plan, and fund an expedition to observe European artillery tactics.

[26] Immediately after establishing his headquarters at Yorktown, Magruder surveyed the region and found the circumstances favorable: the marshy terrain, dense undergrowth, and watercourses led him to surmise that a successful defense of the Peninsula was plausible.

Civilian intelligence reports and a friendly fire incident during the night exposed the position of Butler's troops whose initial advance and subsequent thrusts were thwarted despite a Confederate disadvantage of manpower.

[32] His victory reaffirmed the belief of many southerners in the Confederate cause, and Civil War historian Douglas Southall Freeman wrote Magruder was one of its earliest heroes—"second only to Beauregard in the esteem of the Confederacy" prior to the Seven Days Battles.

[36] Following the withdrawal of the Army of Northern Virginia, under Maj. Gen. Joseph E. Johnston, south of the Rappahannock River, Maj. Gen. George B. McClellan revised plans for the spring offensive.

4 and 5, united by long curtains and flanked by rifle-pits, form the left of the line, until at the commencement of the military road it reaches the Warwick River, here a sluggish and boggy stream, twenty or thirty yards wide, and running a dense wood fringes by swamps.

[41]Two garrisons, amounting to 6,000 men, were stationed at Gloucester Point and Mulberry Island with heavy artillery to block Union passage of the York and James Rivers.

[44] As Union forces emerged from patches of woods on Magruder's right flank and towards Lee's Mill, artillery and rifle fire erupted to repel Keyes's advance.

[45] Magruder's tactics—the constant marching of his forces and sporadic artillery barrages—created the illusion of a much larger military presence and persuaded McClellan to call for a siege of Yorktown.

On arrival, he received a leave of absence from Johnston to seek medical treatment at Westover; Maj. Gen. David Rumph Jones replaced Magruder in command.

[50] In his memoirs, President Jefferson Davis wrote Magruder's absence from the Battle of Williamsburg on May 5 was regrettable, "as it appears that the positions of the redoubts he had constructed were not all known to the commanding General [Johnston], and some of them being unoccupied were seized by the enemy".

[53] On May 31, Johnston massed the divisions of Major Generals James Longstreet, D. H. Hill, and Benjamin Huger as part of a bold offensive toward Seven Pines, which aimed at isolating two Union corps south of the Chickahominy and overwhelming them.

[56] Lee hastened forward his plans for an attack on McClellan's right flank, finding his left heavily fortified following Seven Pines and "injudicious, if not impracticable" for an assault.

[62] Lee, having ascertained by the night of June 28 that McClellan was in retreat, ordered Magruder the next day in immediate pursuit along the Williamsburg Road and York River Railroad.

[69] Thus, Magruder led charges on Malvern Hill, initially with brigades under Huger's command; he impatiently rushed his straggling men into the battle as they arrived to the field, failing to break through the Union's defensive works.

[85] Before fleeing to Havana, Magruder appealed to Maximillian I to escape the country; the Emperor refused to abandon his followers, fell under siege in Querétaro, and was executed on June 19, 1867.

[87] In 1869, Magruder was invited to lecture in New Orleans on Mexican politics, speaking "kindly of the well-intentioned emperor [Maximillian I] and his ambitious wife and judged that they were genuinely concerned about the welfare of Mexico".

[93] As a leader, Magruder was an "experienced artillery officer of shrewd intelligence", developed an ability to deliver charismatic speeches, and was quick to credit his men for his successes.

[96] Later, as he reflected in his 1874 book Narrative of Military Operations, Johnston wrote Magruder's efforts on the Virginia Peninsula "saved Richmond and gave the Confederate government time to swell that officer's handful to an army".