Pierpont was born in Monongalia County, Virginia (now West Virginia), on January 25, 1814. He spent his youth in Fairmont, Virginia (also in what is now West Virginia), and, from 1835 until 1839, attended Allegheny College in Meadville, Pennsylvania. After a brief stint as a teacher, Pierpont began his legal career in trans-Allegheny Virginia representing such influential clients as the. Pierpont, along with partner James Otis Watson, became one of Virginia’s earliest coal operators. A lifelong Methodist, he married Julia Augusta Robertson on December 26, 1854.
Pierpont’s political career began in 1840 when he made speeches across western Virginia in support of Whig presidential nominees William Henry Harrison of Ohio and fellow Virginian. During the , he campaigned for Constitutional Union nominees John Bell of Tennessee and Edward Everett of Massachusetts. (The Constitutional Union Party attracted conservative Southern members of the Whig Party and anti-immigrant Know Nothings who sought to emphasize the Union and downplay slavery.) During the secession crisis of 1860 and 1861, Pierpont delivered pro-Union, antislavery addresses to large crowds across northwestern Virginia.
After meeting since February, thein voted to secede in April 1861. This prompted the still-Unionist western delegates of the state to organize the First Wheeling Convention (May 13–15, 1861). During the meeting, Pierpont promoted the reorganization of the state government, and following the passage of the by statewide referendum on May 23, Pierpont was elected to attend the Second Wheeling Convention (June 11–25, 1861). On June 20, he was unanimously elected governor of the Restored government of Virginia.
The city of Wheeling initially served as the headquarters of the Restored government of Virginia, but after the formation of West Virginia on June 20, 1863, and Pierpont’s reelection as governor that December (governor, that is, of the Restored government and not of West Virginia), the reorganized state government relocated to Alexandria. Pierpont dedicated his energies to raising troops and funds for the Union war effort, coordinating with U.S. president Abraham Lincoln‘s administration, combating Confederate sympathizers, and working to return Virginia to the Union. Pierpont promoted the creation of “free schools,” the extension of constitutional rights to, and in 1864 the convening of a aimed at abolishing slavery.
After the conclusion of the Civil War, the Alexandria government moved to Richmond, where Pierpont began the process of reconstructing Virginia. Pierpont and his civilian administration oversaw local and state elections, promoted the rights of freedmen, and worked to rebuild the state’s economy. Due to his conciliatory policies toward ex-Confederates, Pierpont was criticized by Radical Republicans. In March 1867, the United States Congress, as part of its new Reconstruction policy, placed Virginia under the military command of General John M. Schofield. Despite his protestations, Pierpont was removed from office on April 4, 1868.
After his ouster, Pierpont quietly returned to Fairmont, where his support for the statehood movement earned him election by Marion County voters to the West Virginia state senate in 1869. Due to the increasing Democratic control of the state government, he was not reelected in 1870 and subsequently retired from politics. Pierpont spent the final years of his life as a founder and member of the West Virginia Historical Society. He died in Pittsburgh, Pennsylvania, on March 24, 1899.