He served in the army of the Confederate States of America, fighting in the 1862 Peninsula Campaign and played a prominent role in the Battle of Gettysburg.

[1] He earned praise for his achievements from President James K. Polk, who appointed him an assistant professor at the United States Naval Observatory.

[4] Pettigrew studied law, traveled to Europe, and eventually moved to Charleston, South Carolina, where he worked in the legal field with his uncle, James Louis Petigru.

[6][1] While in office, he presented a report opposing the resumption of the international slave trade, which, along with his participation as a second in a duel, lead to Pettigrew losing his reelection attempt.

Pettigrew ordered the occupation of Castle Pinckney, and was stationed with the South Carolina forces at Charleston Harbor through the Battle of Fort Sumter in April 1861.

[7] Confederate President Jefferson Davis urged him to accept higher command, but he declined because of his lack of military experience.

Both Heth's division and Hill's corps were new organizations, having been created as part of Lee's reorganization following the death of Stonewall Jackson.

[16] Pettigrew's old brigade, now commanded by James K. Marshall, had been roughly handled on the first day of the battle, and was not in good condition for the charge.

Union cavalry probed the southern defenses throughout the night as Lee's army crossed the pontoon bridges into West Virginia.

On the morning of July 14, 1863, Pettigrew's brigade was one of the last Confederate units still north of the Potomac River when the Union attacked his position.

[19] On foot and in the front line, Pettigrew was directing his soldiers when he was shot by a Union cavalryman from the Michigan Brigade at close range, the bullet striking him in the abdomen.