William Appo was born in Philadelphia around 1808 to St. Appo and Ann Appo. A gifted musician, he emerged as a pianist, hornist, conductor, and respected music teacher. By the 1820s he was performing at the Walnut Street Theatre in Philadelphia, and from 1837–1838 he toured England with Francis Johnson’s Philadelphia Military Band, performing for Queen Victoria at Buckingham Palace.
Appo married Suzanne Elisabeth Henry in 1828, divorcing two years later. In 1836 he married Elizabeth, a schoolteacher in Washington, D.C., and together they raised four children: Ellen, Catherine, William, and John. He purchased land in North Elba, New York, in 1848, linking him to the community later associated with John Brown and free Black settlement.
Throughout the 1850s and 1860s Appo continued teaching music, accumulating modest real and personal estate holdings. Census records place him in Burlington, New Jersey, in 1860 with three children—Catherine, Garnet, and infant Henry Simson. By 1870 he was living alone in New York City, but he later returned to North Elba, where he married Albertine Eppers Thompson and welcomed their daughter, also named Albertine.
Appo died in North Elba on January 19, 1880, at the age of about 72 from paralysis. He was buried in the town cemetery, leaving behind a legacy as one of the earliest documented African American professional musicians connected to the North Elba community.