William Forsyth (1737–1804) was a Scottish botanist. He was a royal head gardener and a founding member of the Royal Horticultural Society. A genus of flowering plants, Forsythia, is named in his honor.
Forsyth was born at Oldmeldrum in Aberdeenshire, and trained as a gardener at the Chelsea Physic Garden where he became a mentor to John Fraser. In 1779, he was appointed superintendent of the royal gardens at Kensington and St James'.
His great-grandson was the gardener and landscape architect Joseph Forsyth Johnson (1840–1906). Johnson was in turn the great-grandfather of the entertainer Bruce Forsyth.