[2] McDowell initially attended the College de Troyes in France before graduating from the United States Military Academy in 1838, where one of his classmates was P. G. T. Beauregard, his future adversary at First Bull Run.

[3] Between 1848 and 1861, McDowell generally served, as a staff officer to higher-ranking military leaders and developed experience in logistics and supply.

His strategy during the First Battle of Bull Run was imaginative but ambitiously complex, and his troops were not experienced enough to carry it out effectively, resulting in an embarrassing rout.

Because of his actions at Cedar Mountain, McDowell was eventually brevetted major general in the regular army; however, he was blamed for the subsequent disaster at Second Bull Run.

He escaped culpability by testifying against Major General Fitz John Porter, whom Pope court-martialed for alleged insubordination in that battle.

On December 16, 1872, McDowell succeeded General George G. Meade as commander of the Military Division of the South and remained until June 30, 1876.

In 1879, when a board of review commissioned by President Rutherford B. Hayes issued its report recommending a pardon for Fitz John Porter, it attributed much of the loss of the Second Battle of Bull Run to McDowell.

Following his retirement from the army, General McDowell exercised his fondness for landscape gardening, serving as Park Commissioner of San Francisco, California until his death from heart attack on May 4, 1885.