Humphry Marshall was born at Derbydown Homestead in the village of Marshallton, Pennsylvania (within West Bradford Township) on October 10, 1722. He was the cousin of botanists John Bartram and William Bartram. Like many early American botanists, he was a Quaker.
Marshall received the rudiments of an English education, and was apprenticed to the business of a stonemason, which trade he subsequently followed. Soon after his marriage in 1748 to Sarah Pennock he took charge of his father's farm, and about that time began to devote his attention to astronomy and natural history, building a small observatory in one corner of his residence. He specialized early in native plants, after gaining his enthusiasm for botany from John Bartram. In 1767 he came into the possession of the family estate, and in 1773 he created a botanical garden at Marshallton with both native and exotic plants. This was the second in the United States, the first having been established by John Bartram. As late as 1849, many of the plants still survived, although neglect had turned the garden into a mere wilderness.
In 1785, Marshall published "Arboretum Americanum: the American Grove, an Alphabetical Catalogue of Forest Trees and Shrubs, Natives of the American United States" (Philadelphia). For many years, he was the treasurer for Chester County and trustee of the public loan office. In 1768, he was elected a member of the American Philosophical Society, and he was a member of other scientific societies.
Marshall's first wife died in 1786; he married Margaret Minshall in 1788. He had no children by either wife. In his later years, he was partly blinded by cataracts. Marshall died on November 5, 1801. In 1848 the Borough of West Chester named the public square the Marshall Square in his honor.
Marshall has been called the "Father of American Dendrology".
A genus of plants, Marshallia, was named in honor of Humphry Marshall and his nephew Moses Marshall, also a botanist.
Marshall Square Park in the Borough of West Chester, Pennsylvania, is four miles east of Marshallton where Humphry Marshall was born; the Park's founders named the square after their 18th century predecessor. On June 27, 2007 — proclaimed Humphry Marshall Day by Borough Mayor, Dick Yoder — a long-overdue marker honoring the Park's namesake was unveiled.
- "National Historic Landmarks & National Register of Historic Places in Pennsylvania" (Searchable database). CRGIS: Cultural Resources Geographic Information System. Note: This includes Pennsylvania Register of Historic Sites and Landmarks (August 1971). "Pennsylvania Historic Resource Survey Form: Derbydown Homestead" (PDF). Retrieved 2012-12-15.
- American Philosophical Society Archives. Appleton's entry is incorrect. Wilson, James Grant; Fiske, John, eds. (1900). "Marshall, Humphrey". Appletons' Cyclopædia of American Biography. New York: D. Appleton.
- "Author Query for 'Marshall'". International Plant Names Index.