After admission to the Virginia bar, Harrison crossed the Appalachian Mountains and began his legal practice in Parkersburg in 1819, where Judge Daniel Smith found him qualified. He may also have practiced in Marietta, Ohio across the Ohio River. In 1821, Harrison moved to Clarksburg, the center of that Virginia judicial circuit. In 1823, Harrison became an assistant U.S. Attorney for the Western District of Virginia and traveled on horseback back across the Appalachians to Wythe County, Virginia each year, until a court of appeals was founded in Lewisburg in Greenbrier County. After his federal post ended, Harrison had a private legal practice, as well as represented Harrison County for three terms in the Virginia House of Delegates at various times alongside legislative veterans Daniel Kincheloe, Wilson K. Shinn and Jessee Flowers. Harrison's legislative service ended when he became the Harrison County Commonwealth attorney. In 1841, Harrison attended a convention at his Clarksburg Presbyterian church presided over by his fellow lawyer George Hay Lee, which sought to convince the Virginia General Assembly to fund free public schools, although such would become a reality only after the Civil War. Harrison opposed secession and attended a peace conference in Washington D.C. in February 1861, which convinced him that many secessionists were motivated by a lust for power and self-aggrandizement. When Virginia seceded, Gideon D. Camden, the local judge since 1855 sided with the secessionists and would be elected to the First Confederate Congress, and his son Gideon D. Camden Jr. may have organized a Confederate infantry unit. In the fall of 1861, Harrison succeeded Camden by winning election as judge for the 21st circuit. The Wheeling Convention later appointed Harrison a member of the Governor's Council, where he helped establish the new state's justice system. His son Thomas Willoughby Harrison would become of member of the new state's first constitutional convention. As West Virginia became a state in its own right, the Union Convention nominated Harrison as one of the first three judges of the new Supreme Court of Appeals. On June 20, 1863, as the eldest member of the new court, Judge Harrison led his fellow appeals judges draw lots as to term length. Berkshire drew the shortest term of office, four years, but was also chosen to lead the body. Edwin Maxwell, a fellow Republican from Harrison County defeated Berkshire in 1866. Harrison resigned and Berkshire was appointed to serve the rest of his term, thus maintaining the court's geographic diversity.
Personal life
On November 19, 1823, Harrison married Anna Mayburry, whose family had long operated iron furnaces in Pennsylvania and Maryland before moving to Clarksburg, where her father ran a hotel on what became the site of the Harrison County courthouse and would later operate a furnace in Rockingham County, Virginia before his death. They would have 11 children: Thomas Willoughby Harrison, Matthew Waite Harrison, Frederick Jones Harrison, Charles Tyler Harrison, William Gustavus Harrison, Mayburry M. Harrison, Susan Ellen Harrison, Elizabeth Jones Harrison, Llewellyn Cuthbert Harrison, Sarah Jane "Sallie" Harrison and Anna Rebecca Harrison. William Harrison's never-married elder brother Frederick T. Harrison lived with the family for 63 years, including after the death of their mother in Clarksburg.
Death and legacy
William A. Harrison died on New Year's eve, 1870 and was survived by his widow, his bachelor brother Frederick, and numerous children and grandchildren. His son Thomas Willoughby Harrison had become Harrison County's first West Virginia circuit judge, and served until after adoption of the state's new constitution in 1872, after which Democrats replaced Republicans like the Harrisons, although his grandson S.W. Harrison would later become Clerk of the U.S. Circuit Court.
