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 as chief superintendent of the royal gardens at Kensington and St James’s.
His great grandson was the gardener and landscape architect Joseph Forsyth Johnson (1840–1906). He in turn was the great grandfather of the entertainer Bruce Forsyth.