He was the youngest brigade commander and only non-professional general officer in the division that led Pickett's Charge, during which he was severely wounded.

By the time young James was born, his paternal grandmother and four aunts also lived at the plantation William Kemper had bought for $5,541.40 in 1800.

His maternal great-grandfather, Col. John Jasper Stadler, had served on George Washington's staff as a civil engineer and planned fortifications in Maryland, Virginia, and North Carolina during the American Revolutionary War, and his grandfather John Stadler Allison served as an officer in the War of 1812 but died when his daughter Maria was very young.

Still, his father and a neighboring planter, Henry Hill of Culpeper, founded Old Field School on the plantation to educate local children, including A.P.

At Washington College's graduation ceremony in 1842, 19-year-old Kemper gave the commencement address, taking for a topic "The Need of a Public School System in Virginia."

Kemper then returned home, where he joined a Tee-Total (Temperance) Society as well as studied law under George W. Summers of Kanawha County (a former U.S. Representative), after which Washington College awarded him a Master's degree in June 1845.

Kemper and his friend Birkett D. Fry of Kanawha County traveled to the national capital on December 15, 1846, hoping to secure commissions in the First Regiment of Virginia Volunteers.

During the Mexican–American War, Kemper received favorable reviews and met many future military leaders, but his unit arrived just after the Battle of Buena Vista and mainly maintained a defensive perimeter in Coahuila province.

He represented many fellow veterans making land claims, as well as speculated in real estate and helped form the Blue Ridge Turnpike Company (between Gordonsville and the Shenandoah Valley.

Promoting himself as proslavery, anti-abolitionist, and pro-states' rights, Kemper defeated Marcus Newman and was elected to represent Madison County in the Virginia House of Delegates in 1853 (the year his father died at age 76).

At the Battle of Seven Pines, Kemper's brigade attempted to relieve General D.H. Hill's battered troops but retreated from massed enemy artillery fire and did not engage the U.S. infantry.

At the Battle of Antietam, Kemper was positioned south of the town of Sharpsburg, defending against Major General Ambrose E. Burnside's assault in the afternoon of September 17, 1862.

Another army reorganization after Antietam led to Kemper's brigade being placed in a division commanded by Brigadier General George Pickett, who had been on medical leave since being wounded at Gaines Mill.

After crossing Emmitsburg Road, the brigade was hit by flanking fire from two Vermont regiments, driving it to the left and disrupting the cohesion of the assault.

This act of bravado made Kemper an obvious target, and he was wounded by a bullet in the abdomen and thigh before being captured by U.S. soldiers.

In 1869 Kemper allied with another former Confederate general turned railroad entrepreneur William Mahone to elect Gilbert C. Walker to the Virginia House of Delegates.

[11] After his wife Bella[12] died in September 1870 of complications from the birth of their seventh child, Kemper's political activities increased.

[12] Kemper ran for Congress in the 7th Congressional District (after the redistricting caused by the 1870 census) but lost to incumbent John T. Harris of Harrisonburg.

Kemper's supporters included former Confederate Generals Jubal Early and Fitzhugh Lee as well as Mahone and noted raider John Singleton Mosby.

His last major public reception, in October 1877, hosted President Rutherford B. Hayes, who opened the state fair in Richmond.

[13] As his term of office ended (the state Constitution forbidding his re-election), Kemper (with his six surviving children and various domestic animals) returned to farming and his legal practice.