

The son of missionaries, Armstrong was born January 30, 1839 in Maui, Hawaii, the sixth of ten children. He attended Punahou School in Honolulu, Hawaii. In 1860 his father suddenly died, and Armstrong, at age 21, left Hawaii for the United States and attended Williams College in Massachusetts, graduating in 1862.

After graduating college, Armstrong volunteered to serve in the Union Army during the American Civil War, and recruited a company near Troy, New York. He was appointed a captain in the 125th New York Infantry, a three-years regiment in George L. Willard's brigade. Armstrong was among the 12,000 men captured in September 1862 with the surrender of the garrison at Harpers Ferry. After being paroled,he returned to the front lines in Virginia in December. As part of the 3rd Division of the II Corps under Alexander Hays Armstrong fought at the Battle of Gettysburg in July 1863, defending Cemetery Ridge against Pickett's Charge.

Armstrong subsequently rose through the ranks to lieutenant colonel, being assigned to the 9th Regiment, United States Colored Troops (USCT) in late 1863. He was assigned command of the 8th U.S. Colored Troops when its previous commander was disabled from wounds. Armstrong's experiences with these regiments aroused his interest in the welfare of black Americans. He led the regiment during the Siege of Petersburg, and the 8th was one of the first Union regiments to enter the city after the Confederates withdrew from their trenches. In November 1864, Armstrong was promoted to colonel "for gallant and meritorious services at Deep Bottom and Fussell's Mill" during the Siege of Petersburg.

The 8th USCT pursued the Army of Northern Virginia during the subsequent Appomattox Campaign. After Robert E. Lee surrendered that army, Armstrong and his men returned to Petersburg briefly before being sent by sea to Ringgold Barracks near Rio Grande City on the Mexican border in Texas. Armstrong was awarded the brevet rank of brigadier general of volunteers. On October 10, 1865, the 8th USCT began marching from Texas to Philadelphia, where Armstrong and his men were discharged out of the military in December shortly after their belated arrival.

When Armstrong was assigned to command the USCT, training was conducted at Camp Stanton near Benedict, Maryland. While stationed at Stanton, he established a school to educate the black soldiers, most of whom had no education as slaves.

At the end of the war, Armstrong joined the Freedmen's Bureau. With the help of the American Missionary Association, he established the Hampton Normal and Agricultural Institute – now known as Hampton University – in Hampton, Virginia in 1868. The Institute was meant to be a place where black students could receive post-secondary education to become teachers, as well as training in useful job skills while paying for their education through manual labor.

During Armstrong's career, and during Reconstruction, the prevailing concept of racial adjustment promoted by whites and African Americans equated technical and industrial training with the advancement of the black race. This idea was not a new solution and traced its history to before the American Civil War. But especially after the war, blacks and whites alike realized the paradox that freedom posed for the African American population in the racist south. Freedom meant liberation from the brutality and degradation of slavery, but as W.E.B. DuBois described it, a black person "felt his poverty; without a cent, without a home, without land, tools, or savings, he had entered into competition with rich, landed, skilled neighbors. To be a poor man is hard, but to be a poor race in a land of dollars is the very bottom of hardships." Although the end of slavery was the inevitable result of the Union victory, less obvious was the fate of millions of penniless blacks in the South. Former abolitionists and white philanthropists quickly focused their energies on stabilizing the black community, assisting the newly freed blacks to become independent, positive contributors to their community, helping them improve their race and encouraging them to strive toward a standard put forth by American whites.

In the aftermath of Nat Turner's slave rebellion in 1831, the Virginia General Assembly passed new legislation making it unlawful to teach slaves, free blacks, or mulattoes to read or write. Similar laws were also enacted in other slave-holding states across the South. The removal of these laws after the Civil War helped draw attention to the problem of illiteracy as one of the great challenges confronting these people as they sought to join the free enterprise system and support themselves.

One instrument through which this process of racial uplift could take place was schools such as the Hampton Normal and Industrial Institute. At the heart of the early Hampton-style education during Armtrong's tenure was this emphasis on labor and industry. However, teaching blacks to work was a tool, not the primary goal, of the Institute. Rather than producing classes of individual craftsmen and laborers, Hampton was ultimately a normal school (teacher's school) for future black teachers. In theory, these black teachers would then apply the Hampton idea of self-help and industry at schools throughout the U.S., especially the South. To this end, a prerequisite for admission to Hampton was the intent to become a teacher. In fact, approximately 84 percent of the 723 graduates of Hampton’s first twenty classes became teachers. Armstrong strove to instill in these disciples the moral value of manual labor. This concept became the crucial component of Hampton’s training of black educators.

Perhaps the best student of Armstrong’s Hampton-style education was Booker T. Washington. After coming to the school in 1872, Washington immediately began to adopt Armstrong’s teaching and philosophy. Washington described Armstrong as “the most perfect specimen of man, physically, mentally and spiritually the most Christ-like….” Washington also quickly learned the aim of the Hampton Institute. After leaving Hampton, he recalled being admitted to the school, despite his ragged appearance, due to the ability he demonstrated while sweeping and dusting a room. From his first day at Hampton, Washington embraced Armstrong's idea of black education. Washington went on to attend Wayland Seminary in Washington, D.C., and he returned to Hampton to teach on Armstrong's faculty. Upon Sam Armstrong's recommendation to Lewis Adams, Washington became the first principal of a new normal school in Alabama, which became Tuskegee University. Many religious organizations, former Union Army officers and soldiers, and wealthy philanthropists were inspired to create and fund educational efforts specifically for the betterment of African Americans in the South by the work of pioneering educators such as Samuel Armstrong and Dr. Washington.

Samuel Armstrong suffered a debilitating paralysis in 1892 while speaking in New York. He returned to Hampton in a private railroad car provided by his multimillionaire friend, Collis P. Huntington, builder of the Chesapeake and Ohio Railway and Newport News Shipbuilding and Drydock Company, with whom he had collaborated on black-education projects.

Samuel Chapman Armstrong died at the Hampton Institute on May 11, 1893, and is buried in the Hampton University Cemetery.